Multi-material multi-component spinal implant

ABSTRACT

An implantable medical device, such as an intervertebral spacer, may comprise a polymeric component and a metallic component. The metallic component can contain both porous metal and substantially-solid metal. The polymeric material can contain particles of an osseointegrative material. The metallic component can be more protruding toward bone than the polymeric component while having a smaller dimension of roughness than the polymeric component. In embodiments, the pin may press-fit against substantially solid metal. The porous metal may surround solid metal which in turn may surround the pin. The pin may have a press-fit with metal and a looser fit with polymeric component, if the metal components and polymeric components are trapped. A pin may connect superior and inferior metal components by a press-fit. The central opening may be exposed to porous metal and also to substantially-solid metal and to polymer. Specific geometries of implants are disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a Continuation-In-Part of U.S. Ser. No.17/143,649 filed Jan. 7, 2021. U.S. Ser. No. 17/143,649, in turn, is adivisional of U.S. Ser. No. 16/169,481 filed Oct. 24, 2018, which inturn claims the benefit of US Provisional patent application U.S. Ser.No. 62/576,203, filed Oct. 24, 2017. All of these are incorporatedherein by reference in their entireties.

FIELD OF THE INVENTION

Embodiments of the invention pertain to spinal implants.

BACKGROUND OF THE INVENTION

Numerous designs of spinal implants exist. However, it is stilldesirable to optimize osseointegration and to improve certain designfeatures.

SUMMARY OF THE INVENTION

In an embodiment of the invention, there may be provided an implantabledevice, the device comprising a polymeric component having a polymericcomponent bone-facing surface and a metallic component having a metalliccomponent bone-facing surface, the polymeric component and the metalliccomponent being mechanically joined to each other, the device having anexternal bone-facing surface that is partially the polymeric componentbone-facing surface and partially the metallic component bone-facingsurface adjacent to the polymeric component bone-facing surface, whereinthe metallic component bone-facing surface is more protruding from thedevice in a bone-facing direction than is the polymeric componentbone-facing surface, and wherein the polymeric component bone-facingsurface has polymeric roughness features on a larger dimensional scalethan metallic roughness features of the metallic component bone-facingsurface.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, thedevice comprising a polymeric component, the device comprising ametallic component, the metallic component and the polymeric componentbeing mechanically connected to each other, wherein the metalliccomponent comprises a substantially solid region and a porous region,the substantially solid region and the porous region being integrallyadjoined to each other, wherein one of the bone-facing surfaces of thedevice comprises a surface of the polymeric component and a surface ofthe porous region of the metallic component and a surface of thesubstantially solid region of the metallic component.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, thedevice comprising a polymeric component, the device comprising ametallic component, the metallic component and the polymeric componentbeing mechanically connected to each other, wherein the metalliccomponent comprises a substantially solid region and a porous region,the substantially solid region and the porous region being integrallyadjoined to each other, the substantially solid region having a densityat least 90% of a solid density of a metal of which the metalliccomponent is made, the porous region having a density less than 80% ofthe metal of which the metallic component is made, wherein in themetallic component, the porous region is part of one of the bone-facingsurfaces, and the porous region also faces the central opening.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, thedevice comprising a polymeric component and a first metallic componenton the first bone-facing surface and a second metallic component on thesecond bone-facing surface, further comprising a pin, wherein the pinoccupies a hole in the first metallic component and occupies a hole inthe second metallic component and occupies a hole through the polymericcomponent, wherein the pin is mechanically joined to the hole in thefirst metallic component and the pin is mechanically joined to the holein the second metallic component.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, thedevice comprising a polymeric component, the device comprising ametallic component that is mechanically connected to the polymericcomponent, wherein the metallic component comprises a substantiallysolid region and a porous region, wherein the porous region of themetallic component has a density less than 80% of a density of metal ofwhich the metallic component is made, and the substantially solid regionhas a density more than 90% of a density of metal of which the metalliccomponent is made, wherein the metallic component has a metalliccomponent outwardly-facing surface that is part of one of thebone-facing surfaces, and the metallic component has a metalliccomponent inwardly-facing surface opposed to the metallic componentoutwardly-facing surface, wherein the metallic component inwardly-facingsurface has at least a majority of its surface being the substantiallysolid region, wherein the metallic component outwardly-facing surfacecontains both a surface of the porous region and a surface of thesubstantially solid region.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, thedevice comprising a polymeric component, the device comprising a firstmetallic component that is mechanically connected to the polymericcomponent, further comprising a pin that passes through at least onehole in the polymeric component and at least one hole in the firstmetallic component, wherein the pin is a press-fit in one of the holesand is looser than a press-fit in another of the holes, wherein, in theabsence of the pin, the polymeric component and the first metalliccomponent have a relationship with each other that at least partiallyconstrains relative motion between the polymeric component and themetallic component, wherein when the pin is installed, the polymericcomponent and the metallic component are further constrained withrespect to each other.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, thedevice comprising a polymeric component, the device comprising ametallic component, the metallic component and the polymeric componentbeing mechanically connected to each other, wherein the device comprisesat one end a post, the post extending along a direction from the firstbone-facing surface to the second bone-facing surface, the post adaptedto be gripped by an installation instrument, the post having a convexexterior, wherein the post is partially in the metallic component andpartially in the polymeric component.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, whereinthe device comprises at one end a post, the post extending along adirection from the first bone-facing surface to the second bone-facingsurface, the post adapted to be gripped by an installation instrument,the post having a convex exterior, wherein the post comprises flats orcorners or both, and wherein the device comprises an engagement featurethat is in addition to the post.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, thedevice comprising a polymeric component and a metallic component thatare mechanically joined to each other, the metallic component comprisinga substantially solid region and a porous region, wherein one of thebone-facing surfaces that comprises a continuous path of material of theporous region all the way around a circumference of the central opening,and comprises a surface of the polymeric material around a portion ofthe circumference of the central opening, wherein the porous metalprotrudes beyond the polymeric component.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, whereinthe device comprises a first metallic component, a second metalliccomponent, a first side polymeric component and a second side polymericcomponent, wherein the first metallic component is mechanically joinedto the first side polymeric component and to the second side polymericcomponent, and the second metallic component is mechanically joined tothe first side polymeric component and is mechanically joined to thesecond side polymeric component.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, thedevice comprising a metallic component and a remainder of the device,the metallic component and the remainder of the device beingmechanically joined to each other, wherein the metallic componentcomprises an anchoring screw hole passing through an anterior surface ofthe metallic component and continuing at least partially through thebone-facing surface, the anchoring screw hole having an anchoring screwhole internal surface, wherein the bone-facing surface comprises asubstantially-solid metal region and a porous metal region, and whereinthe porous metal region is located such that no portion of an anchoringscrew hole internal surface comprises any of the porous metal region, orno more than 10% of the anchoring screw hole internal surface comprisesthe porous metal region.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, thedevice comprising a metallic component and a remainder of the devicethat are mechanically joined to each other, the metallic componentcomprising a full-height portion of the metallic component extendingcontinuously from the first bone-facing surface to the secondbone-facing surface, and further comprising a superior extension and aninferior extension defining a split space therebetween, wherein themetallic component comprises a porous metal region that exists, on thebone-facing surface, in both the full-height portion of the metalliccomponent and the extension.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, thedevice comprising a metallic component and a remainder of the device,the metallic component and remainder of the device being mechanicallyjoined to each other, wherein, the metallic component, in the firstbone-facing surface, comprises a porous metal region, and the porousmetal region is surrounded on its entire perimeter on the bone-facingsurface by a frame of substantially-solid metal. Within the porous metalregion there may also be a solid metal region on the bone-facingsurface, such as to surround a dowel pin.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, thedevice comprising a metallic component and a remainder of the device,the metallic component and the remainder of the device beingmechanically joined to each other, wherein the bone-facing surfacecomprises a substantially solid metal region and a porous metal region,wherein along a line passing through the device in a generally lateraldirection, there is the following sequence of materials: polymericmaterial; substantially-solid metal; porous metal; substantially-solidmetal; the central opening; substantially-solid metal; porous metal;substantially-solid metal; and polymeric material.

In an embodiment of the invention, there may be provided an implantabledevice, the device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromthe first bone-facing surface to the second bone-facing surface, thedevice comprising an anterior component and a remainder of the device,the anterior component and the remainder of the device beingmechanically joined to each other, wherein the device comprises at leastone anchoring screw situated in an anchoring screw hole in the anteriorcomponent, wherein the anterior component comprises an anterior holeoriented in a generally anterior-posterior direction, wherein theanterior hole comprises internal threads at an anterior portion thereofsuitable to engage with an installation instrument, and comprises aposterior recess, the posterior recess having an internal diameter thatis greater than a minor diameter of the internal threads, furthercomprising a screw retention cover that, when in desired position,blocks a head of the anchoring screw from passage out of the anchoringscrew hole, wherein the screw retention cover is able to engage with theinterior threads or with the posterior recess to secure the cover deviceto the anterior component. In an embodiment, the screw retention covermay have a threaded post or may have a post that is split so as to beable to deflect suitably to enter the narrowest part of the anteriorhole, and then to spring outward after passing through the narrowestpart of the anterior hole.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

Embodiments of the invention are further described but are in no waylimited by the following illustrations.

FIG. 1A is a three-dimensional view showing an implant suitable forPosterior Lumbar Interbody Fusion.

FIG. 1B shows the implant of FIG. 1A viewed mostly from the side, withlocalized views of some height interrelationships.

FIG. 1C shows the polymeric component of the implant of FIG. 1A.

FIG. 1D shows another view of the polymeric component of FIG. 1A.

FIG. 1E shows the non-polymeric components of the implant of FIG. 1A.

FIG. 1F shows the end component of the implant of FIG. 1A, from aperspective different from the perspective of FIG. 1E.

FIG. 1G shows two pads connected by a pin.

FIG. 1H is an exploded view of the metallic pad, in which the porousportion and the substantially-solid portion are shown separated fromeach other.

FIG. 1I is a cross-section showing the holes associated with the“barbell” construct.

FIG. 2A is a three-dimensional view showing an implant suitable forinsertion via an oblique approach.

FIG. 2B shows the implant of FIG. 2A in a view looking approximatelyhorizontally at the longer side of the implant.

FIG. 2C shows the implant of FIG. 2A in a view looking approximatelyhorizontally at the leading end of the implant.

FIG. 2D is similar to FIG. 2C except at a slightly different viewingangle.

FIG. 2E is shows the implant of FIG. 2A looking partly at the end thatis suitable to be grasped by an installation instrument, i.e., the endopposite the end shown in FIGS. 2C-2D, but also showing some of the sideof the implant.

FIG. 2F shows the polymeric component of the implant of FIG. 2A.

FIG. 2G shows the non-polymeric components of the implant of FIG. 2A.

FIG. 2H shows another view of the trailing end component of the implantof FIG. 2A.

FIG. 3A is a three-dimensional view of an implant suitable forTransforaminal Lumbar Interbody Fusion.

FIG. 3B shows the polymeric component of the implant of FIG. 3A.

FIG. 3C shows the non-polymeric components of the implant of FIG. 3A.

FIG. 3D shows the trailing end component of the implant of FIG. 3A.

FIG. 3E shows a section of the polymeric component of the implant ofFIG. 3A.

FIG. 3F shows another section component of the implant of FIG. 3A.

FIG. 3G shows a section through the polymeric component of the implantof FIG. 3A, taken at the midplane.

FIG. 3H is similar to FIG. 3G, but with the post shown as having across-sectional shape that is polygonal.

FIG. 4A is a three-dimensional view showing an implant suitable forinsertion via a lateral approach.

FIG. 4B shows the implant of FIG. 4A from a slightly different view.

FIG. 4C shows the polymeric component of the implant of FIG. 4A.

FIG. 4D shows the non-polymeric components of the implant of FIG. 4A.

FIG. 4E shows views of metallic components at the distal end of theimplant of FIG. 4A.

FIG. 4F shows views of metallic components located between the proximalend and the distal end of the implant of FIG. 4A

FIG. 5A is a three-dimensional view showing an implant suitable for usein the cervical spine. This may be termed a lordotic cervical implant.

FIG. 5B shows the polymeric components of the implant of FIG. 5A.

FIG. 5C shows the non-polymeric components of the implant of FIG. 5A.

FIG. 5D shows an exploded view of the implant of FIG. 5A.

FIG. 5E shows a sectional view of the implant of FIG. 5A.

FIG. 5F is a three-dimensional nearly-frontal view showing anotherimplant suitable for use in the cervical spine. This may be termed aconvex cervical implant.

FIG. 5G is a three-dimensional nearly-side view of the implant of FIG.5F.

FIG. 5H shows a detail regarding the porous region in one of thecervical implants.

FIG. 5I shows another detail regarding the porous region in one of thecervical implants.

FIG. 6A is a three-dimensional view of an implant suitable for AnteriorLumbar Interbody Fusion.

FIG. 6B is a three-dimensional view of the implant of FIG. 6A, from adifferent viewpoint.

FIG. 6C is a side view of the implant of FIG. 6A.

FIG. 6D is an exploded view of the implant of FIG. 6A.

FIG. 6E shows the polymeric component of the implant of FIG. 6A.

FIG. 6F shows the non-polymeric components of the implant of FIG. 6A.

FIG. 7A shows a PLIF implant in relation to a vertebra.

FIG. 7B shows a TLIF implant in relation to a vertebra.

FIG. 7C shows a lateral implant in relation to a vertebra.

FIG. 7D shows a cervical implant in relation to a vertebra.

FIG. 7E shows an ALIF implant in relation to a vertebra.

FIG. 8A shows an implant of an embodiment of the invention.

FIG. 8B shows the implant of FIG. 8A with the anterior component and theposterior component exploded away from each other.

FIG. 8C is a three-dimensional view of the anterior component, lookingposteriorly.

FIG. 8D is a view of the anterior component sectioned through one of theanchoring screw holes.

FIG. 8E is a view of the anterior component sectioned similarly to FIG.8D, but looking in the opposite direction.

FIG. 8F is a view of the anterior component sectioned at its horizontalmidplane.

FIG. 8G is a view of the anterior component sectioned similarly to FIG.8F, but sectioned at a higher elevation.

FIG. 8H is a three-dimensional view of the implant together with itsanchoring screws.

FIG. 8I is a view of an anchoring screw.

FIG. 8J is a sectioned view of an anchoring screw.

FIG. 8K is a section of FIG. 8H, sectioned in a plane that contains oneof the screws.

FIG. 8L is a three-dimensional view of the anterior component with theporous regions shown exploded away from the substantially-solid metalregion.

FIG. 8M is a nearly-top view showing a pair of defined parallel planes.

FIG. 8N is a sectional view through the extensions of the anteriorcomponent, taken posteriorly of the dowel pin.

FIG. 8O is a sectional view through the extensions of the anteriorcomponent, taken through the dowel pin.

FIG. 8P is a view looking generally anteriorly showing the anteriorhole.

FIG. 8Q is a section taken through the anterior hole.

FIG. 8R is a three-dimensional view of the screw-in version of the screwretention cover.

FIG. 8S shows, in cross-section, the screw-in screw retention coverinstalled on the implant.

FIG. 8T is a three-dimensional view of the snap-in version of the screwretention cover.

FIG. 8U shows, in cross-section, the snap-in screw retention coverinstalled on the implant.

FIG. 8V is an external view of either type of screw retention coverinstalled on the implant.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made to FIGS. 1A-7E. In an embodiment of the invention,the anatomy may have a caudal-cephalad direction, and ananterior-posterior direction and a lateral direction. Theanterior-posterior direction may be generally perpendicular to thecephalad-caudal direction. Also, the lateral direction may be generallyperpendicular to the cephalad-caudal direction. Extending along thecephalad-caudal direction of the implant, there may be an open channeltherethrough intended for bone to grow into and through along thecephalad-caudal direction connecting the respective vertebrae.

Generic Components and Features

In an embodiment of the invention, the implant may have one or morecomponents that are made of a polymer. A polymer often used in implants,which has both biocompatibility and good structural strength, ispolyetheretherketone (PEEK). PEEK has an elastic modulus that isreasonably close to the elastic modulus of natural bone, which helps toavoid the problem of stress shielding. PEEK can be considered to beinert with respect to bodily fluids and osseointegration. A furtherpossibility is the use of PEEK that contains granules or particles of anosseointegrative material such as hydroxyapatite (HA). HA is a componentof natural bone and is osteoconductive. HA enhanced PEEK hasosseointegration properties that are superior to those of pure PEEK.Both PEEK and PEEK HA Enhanced are commercially available (asPEEK-Optima and PEEK-Optima HA Enhanced, respectively) from Invibio(West Conshohocken, Pa.). Another such material is available fromDiFusion Technologies (Georgetown, Tex.). In general, osseointegrativematerials that could be used include hydroxyapatite, bioactive glass,and any of the various chemical or crystallographic forms of calciumphosphate.

In embodiments of the invention, the polymeric component may haveengagement features that are truncated pyramids or pyramids, or may haveengagement features that are grooves or ridges that extend in anextruded manner along one direction of the polymeric component. It isalso possible to have both pyramids and grooves, or still other shapes,as engagement features. The engagement features of the polymericcomponent may be suitable to resist motion or expulsion of the implantfrom its implantation site. The dimensions such as height (peak tovalley) or dimension perpendicular to the local implant surface may bein the range of 0.2 mm to 2 mm. Such dimension of the grooves or ridgesor truncated pyramids or similar feature may be larger than thedimension of porosity or roughness of the porous region (if such aregion exists) of the metallic component, and may be larger in generalthan whatever roughness or surface finish exists on any portion of ametallic component of the implant. In an embodiment of the invention,the pyramids are spaced in a pattern of a grid whose spacing ordimensions of repetition of repeating features is 0.5 mm. Moregenerally, the spacing or dimension of repeating pattern may be 0.2 mmto 2 mm. The ratio of feature height to the repeating pattern dimensionmay be in the range of 0.5 to 2.

In an embodiment of the invention, the implant may have components thatare made of metal. Metals, such as titanium and its alloys, haveadvantageous properties of strength and biocompatibility, although insome applications their elastic modulus is so much greater than theelastic modulus of natural bone that there can be a stress shieldingproblem. In any one or more or all of the metallic components, the metalmay comprise a region that is a substantially solid metal and anotherregion that is a porous construct of the same metal as the solid region.Such regions may be joined to each other or may be formed integrallywith each other. Porous metal, especially porous metal that is titaniumor titanium alloys, is considered to have good osseointegrativeproperties. Solid metal is generally considered to have good strengthand toughness, among other properties. A substantially-solid region maybe considered to be a region that has a density that is greater than 90%of the theoretical solid density of the same substance. In the porousregion, it is typical that the porosity of the porous region might beabout 50%, or more generally the density of the porous region may bebetween 40% and 80% of the theoretical solid density of the samesubstance. A typical pore size in the porous region may be between 100microns and 700 microns. All of the pores may be in such size range, ora majority of the pores may be in such size range. Dimensions of surfaceroughness of the porous region may be similar to the pore sizedimensions. Pores may be open pores, i.e., connected with each other,although they do not have to be.

The roughness of the bone-facing surface of the polymeric component canbe rougher or larger than the roughness of the metallic component, whichmay have some or all of its bone-facing surface being porous. Thiscomparison can be judged using the maximum-to minimum (peak-to-valley)height dimension of features in the surface of the polymeric component,and using pore size of the porous region in the metallic component, orother appropriate descriptor of the properties of the bone-facingsurface of the metallic component. The pore size of the porous region ofthe metallic component may, for example be in the range of from 100microns to 700 microns. This may be determined by the particle sizes inthe metal powder initially used in a manufacturing process, theprocessing parameters during additive manufacturing, and othervariables. The features in the polymeric part may be machined, forexample. The maximum-to minimum (peak-to-valley) height dimension offeatures in the surface of the polymeric component may be in the rangeof from 0.2 mm to 2 mm. Even though some part of that possible range mayoverlap with the overall possible range of pore sizes in porous metal,it still may be provided, in a particular implant design, that all ofthe polymeric features are larger than the pore size in the porous metalof that particular implant.

Formation of a metallic component that is substantially solid in oneregion and porous in another region may be performed using an additivemanufacturing technique in which particles of powder are joined to otherparticles to form an object. Such joining can be performed by selectivelaser sintering, by electron beam, or by other methods. Powder-basedtechnologies include selective laser sintering (SLS), direct metal laserSintering (DMLS), selective laser melting (SLM), and Electron BeamMelting (EBM). Some of these use concepts comparable to the SLS exceptthat the material is fully melted rather than sintered. The degree ofporosity in any localized place may be controlled, at least in part, bythe amount of energy deposited at a particular location such as usingthe laser beam or electron beam. It is possible to cause sintering inlocations that are desired to be porous, and to cause melting followedby re-solidification in locations that are desired to besubstantially-solid, or to cause varying degrees of sintering in variouslocations. These choices can be made by adjusting the amount of localenergy deposition. It might also be possible to use three-dimensionalprinting onto a powder bed with drops of binder liquid, followed bysintering.

Embodiments of the invention may comprise metallic components in whichthere are provided certain features such as through-holes for screwsthat are intended to engage with bone, backout-prevention devices forsecuring those screws, holes for press-fit pins therethrough, andfeatures that interface with an instrument that is used during insertionof the implant at a surgical site. Such features may be located entirelyor primarily in regions of the metallic component that are substantiallysolid metal regions, rather than porous. Regions that are made ofsubstantially solid metal can be expected to have greater mechanicalstrength than regions that are made of porous metal. Also, for purposessuch as press-fits, regions that are made of substantially solid metalmay have good dimensional accuracy and stability such as for dimensionsof hole diameters, in comparison to similar geometries if such featureswere to be produced in porous metal, although it is not wished to bebound by this theory.

A polymeric component and a metallic component may be mechanicallyjoined to each other as described elsewhere herein.

In an embodiment of the invention, when the components are fullyassembled to each other, the metallic component may protrude to agreater height toward the bone that the bone-facing surface faces,generally along the longitudinal (cephalad-caudal) direction, thannearby components such as a polymeric component. That amount ofprotrusion by which the metallic surface protrudes relative to a nearbyor adjacent polymeric surface may be about 0.25 mm, or more generally,in the range of 0.1 mm to 2 mm. If such nearby or adjacent surface, suchas of a polymeric component, is corrugated or irregular, such protrusionmay be measured relative to an enveloping surface that contacts peaks ofthe corrugated or irregular surface. This is illustrated in FIG. 1B.

Relative positions of components can be defined using a polymeric regionbounding plane that is a best-fit to local peak features of thepolymeric component. For a metallic component, relative positions ofcomponents can be defined using a metallic region bounding plane that isa best-fit to local peak features of the metallic component. Thequantity of such local peak features can be, four example, three or foursuch peak features counted along the external surface of the componentin a direction toward or away from the interface between the polymericcomponent and the metallic component. A similar method may be used inregard to a bounding plane for features in the polymeric component.

The metallic component may have a porous metal region that is externalor bone-facing. Either all or some of the external or bone-facingsurface may be porous. The overall geometry of the metal surface may besuch that the scale of roughness or porosity of the metal surface, ifany, is smaller than the scale of roughness or dimensions of features ofthe polymeric surface that is bone-facing adjacent to the metal surface.

In the polymeric component, the polymeric surface or the bulk polymericmaterial, or both, may contain inclusions of hydroxyapatite or otherosteoconductive or osseointegrative material. The inclusions at thesurface may be exposed at surfaces as a result of the initial process ofmanufacturing the polymeric material, or they may be exposed bymachining or other material removal process subsequent to initialmanufacturing of the polymeric material.

In an embodiment of the invention, attachment of a metallic component toa polymeric component may be done using a pin whose direction isgenerally parallel to the longitudinal (cephalad-caudal) direction ofthe implant. In such a situation, load in a longitudinal direction thatis transmitted from the metallic component to the polymeric componentmay be transmitted by direct contact of surfaces that are somewhatperpendicular to the direction of the force. It is possible for load tobe transmitted by direct bearing of a surface of the metallic componentbearing against a surface of the polymeric component. In such asituation, the pin may serve a function of establishing location. Thepin may also serve to maintain various parts in assembled relation toeach other.

An embodiment of the invention can comprise a metallic component thathas at least one substantially-solid region and at least one porousregion. It is possible that the porous region can be exposed on anexterior-facing surface of the metallic component, and only on anexterior-facing surface of the metallic component. It is possible thatsubstantially-solid region can be exposed on surfaces other than theexterior-facing surface of the metallic component, and also can beexposed on the exterior-facing surface of the metallic componentsurrounded by porous region, and can be exposed on the exterior-facingsurface of the metallic component surrounding the porous region. It ispossible that the surface of the metallic component that is in contactwith the polymeric component may entirely be substantially-solid metal.It is possible that the surface of the metallic component that is incontact with the polymeric component may be a majority ofsubstantially-solid metal.

In an embodiment of the invention, the implant may have a central holeextending therethrough from a first bone-facing surface to a secondbone-facing surface, with the implant forming a closed path around thecentral hole. Proceeding around the closed path at a bone-facingsurface, that is, the bone-facing superior surface or the bone-facinginferior surface of the wall, there may be alternating regions ofpolymeric material and metallic material. Proceeding around the closedpath at a bone-facing surface, there may be a region that is entirelypolymeric at the bone-facing surface, followed by a region that isentirely metallic at the bone-facing surface, followed by a region thatis entirely polymeric at the bone-facing surface. Proceeding around theclosed path at a bone-facing surface, there may be a region that isentirely metallic at the bone-facing surface, followed by a region thatis entirely polymeric at the bone-facing surface, followed by a regionthat is entirely metallic at the bone-facing surface. In connection withsome of the described geometries and implants, at the midplane of theimplant, proceeding around the closed path, there may be a continuouspath of polymeric material.

In embodiments of the invention, the bone-facing surface may comprisepolymeric material and a porous region of a metallic component and asubstantially-solid region of a metallic component. The polymericmaterial may comprise particles or inclusions of an osteoconductivematerial.

In embodiments of the invention, the implant could have a metallic endcomponent joined to a polymeric component in such a way that at someportions of the external perimeter of the implant, there is only metal,no polymer. The metallic end component could have features such as teethto interface with an instrument, holes to interface with an instrument,threads to interface with an instrument, holes for bone screws, holesfor other screws, and other features. The metallic end component couldcomprise both a substantially-solid region and a porous region. Themetallic end component and the polymeric body could be joined by apress-fit pin similar to what is described herein for other purposes.There may be a relationship between the end component and the polymericcomponent such that when the end component and the polymeric componentare assembled to each other even without pins, there is some constrainton their relative motion.

Embodiments of the invention are further described with respect tocertain specific configurations of spinal implants.

PLIF Implant

Referring now to FIGS. 1A-1I, in an embodiment of the invention, theremay be provided an implant 100, which may be suitable for implantationby a Posterior Lumbar Interbody Fusion (PLIF) surgical approach. Such animplant 100 may comprise a polymeric component 110 and metalliccomponents in the arrangement shown.

FIG. 1A shows the PLIF implant 100 including all of its componentsassembled to each other. The implant may have a first bone-facingsurface and a second bone-facing surface opposed to the firstbone-facing surface, and may have a central opening or passageway 106therethrough from the first bone-facing surface to the secondbone-facing surface. FIG. 1C shows the polymeric component 110 only. InFIG. 1D the polymeric component is omitted, and all other components areshown.

As illustrated in FIG. 1C-1D, there may be a polymeric component 110that may make up a majority of the implant 100. The polymeric component110 may exhibit a continuous path of polymeric material, at least on theinterior of the central opening or passageway 106 through the implant100 extending around the interior surface of central hole 106, althoughthere may be localized cutouts. Furthermore, at one end of the implant100 there may be a trailing end component 120 that is a metalliccomponent. The term trailing end may refer to a particular end that isnot the end that initially enters the surgical site, but rather is theend of the implant that is engaged with an installation instrument. Theopposite term, referring to the end that enters the surgical site first,is leading end. The trailing end component 120 may have upper and lowerprotrusions 130, and the polymeric component 110 may have upper andlower recesses 112 dimensioned so as to be able to receive therespective protrusions 130. Furthermore, the protrusions 130 may haveholes 132 therethrough that are suitable to receive pins 134. Thepolymeric component 110 may have a hole(s) 148 also suitable to receivepins 134 when the various parts are in an assembled configuration. Thepins 134 may have a press-fit relation with at least some of thesecomponents.

As shown in FIG. 1E and separately in FIG. 1F, there may be a trailingend component 120, which may be made of metal. Some of the end component120 may be solid metal and other portions of the end component 120 maybe porous metal. Trailing end component 120 may have recesses 122 on itssides that may be suitable to engage with an installation instrument(not illustrated). Trailing end component 120 may also have a centralhole 124 that is suitable to engage with an installation instrument (notillustrated). Central hole 124 may be threaded. Trailing end component120 may have substantially-solid region 126 and porous region 128.Trailing end component 120 may have protrusions 130, which may begenerally rectangular blocks (parallelepipeds) that protrude from agenerally flat surface 138 of the end component 120. The protrusions 130may be made of substantially-solid material. Some part of theprotrusions 130 may be continuous with substantially-solid material inother parts of the end component 120. The protrusions 130 also may beconnected to or continuous with the porous region 128. As illustrated,the protrusions 130 may be connected to or continuous with both thesubstantially-solid region 126 and the porous region 128. Theprotrusions 130 may have therein holes 132 suitable to receive pins 134,which may form a press-fit. FIG. 1E shows pins 134 engaged withprotrusions 130, while FIG. 1F does not show those pins. End component120 may also have surface 138 that faces a corresponding surface onpolymeric component 110.

As can be seen in FIGS. 1D-1F, there may be a relationship between thepolymeric component 110 and end component 120 such that when polymericcomponent 110 and end component 120 are in their assembled relation toeach other even if pins 134 are not present, there are constraints onpossible motion between polymeric component 110 and end component 120.As illustrated, when polymeric component 110 and end component 120 arein their assembled relation to each other, essentially the only degreeof freedom of motion that is permitted is translation along the longdirection of the implant 100, which is a direction of motion that isused in assembling the end component 120 to polymeric component 110 andthat would cause shear of pins 134 if pins 134 were in place. Because ofthe interrelationships between protrusions 130 and recesses 112, theremay be constraint against relative motion of the two parts along thedirection of pins 134. As a result of such constraint, it is sufficientif pin 134 forms a press-fit in only one of the two components 110, 120;it is not necessary for a press-fit to exist between pin 134 and bothpolymeric component 110 and end component 120. For example, a press-fitmight be created between pin 134 and end component 120, while there maybe a looser fit relationship between pin 134 and polymeric component110. The opposite relationship is also possible. Such provision of apress-fit relationship at less than all of the interfaces of pin 134 maybe helpful in reducing the amount of insertion force that is needed toinsert pin 134 (which is of somewhat small diameter and might besusceptible to buckling).

Referring now to FIGS. 1G-1I, there may also be provided metalliccomponents in the form of pads 149 that are exposed on bone-facingsuperior and inferior surfaces of the implant 100. The metalliccomponents that are pads 149 may have substantially-solid regions 150and 152, and porous regions 154. Substantially-solid regions 150 and 152may be connected to each other or integral with each other. Asillustrated, substantially-solid region 152 may be surrounded by porousregion 154. Such relation may be annular, with substantially-solidregion 152 being inside and porous region 154 being outside. Porousregion 154 may also contact substantially-solid region 152, with aninterface that may be a flat interface.

As illustrated, the metallic components may contain asubstantially-solid region 150, 152 and a porous region 154, asdiscussed herein. As illustrated, in the metallic component that is pad149, the material that is in contact with the pin 156 to form thepress-fit is entirely substantially-solid material, even though otherportions of the metallic component are porous regions 154. It isbelieved that having the material immediately adjacent to thepress-fitted pin 156 be substantially-solid material may be advantageousfor achieving an accurately-dimensioned and tightly-fitting press-fit,although it is not wished to be limited to this explanation.

Referring to FIG. 1G-1I, in further detail, there is shown a metalliccomponent which is a pad 149 as previously illustrated in FIGS. 1A, 1E.In FIG. 1H the porous region 154 and the substantially-solid region 150,152 are shown separated or exploded from each other. As illustrated, theporous region 154 and the substantially-solid region 150 have a flatinterface with each other, with the interface plane being generallyhorizontal. It is further illustrated that in the bone-facing portion ofthe pad 149, the porous region 154 surrounds the substantially-solidregion 152. As illustrated, there is a contact interface between theporous region 154 and the substantially-solid region 152 both in oneplane (the plane that is horizontal) and in a second plane that isgenerally perpendicular to the first plane. As illustrated, the secondplane is any plane that is tangent to the cylindrical interface betweenthe porous region 154 and the substantially-solid region 152. Anannular, or partial-annular, relationship between porous region 154 andsubstantially-solid region 152 is also possible. Other configurationsare also possible.

Superior and inferior metallic components in corresponding places may beconnected to each other by a pin 156, which may be press-fit in at leastsome of components that it passes through. Pin 156 may be a press-fit ina hole through substantially-solid regions 150, 152. Press-fitconsiderations are discussed elsewhere herein. The two metalliccomponents (pads 149) and the pin 156 that connects them may, incombination, form what may be termed a “barbell” construct. FIG. 1Gshows the “barbell” construct in isolation, showing an upper metalliccomponent (pad 149) and a lower metallic component (pad 149) and the pin156 connecting them.

As an example of engagement features in the polymeric component 110,peaks 160 may be provided in the polymeric component 110. The peaks 160may be in the form of pyramids or truncated pyramids, or other shapes.The peaks 160 may be configured in a pattern that is a rectangular gridhaving principal axes that are orthogonal to each other. One of theprincipal axes of the grid may be parallel to a principal axis of theoverall implant 100. One of the principal axes of the grid may beperpendicular to a principal axis of the overall implant 100. Yetanother possibility is that engagement features may be ridges thatextend for some distance in one direction. It would also be possible touse a combination of ridges and pyramids or truncated pyramids, or stillother shapes or combinations thereof.

Referring now to FIG. 1B, it is illustrated that at the bone-facingsurface of implant 100, the metallic components such as end component120 or pad 149 may protrude from implant 100 more prominently than thesurface of the polymeric component 110. The metallic components mayprotrude to a greater height toward the bone that the bone-facingsurface faces, generally along the longitudinal (cephalad-caudal)direction, than nearby components such as polymeric component 110. Thedifference, which is labeled in FIG. 1B, may be in the range of 0.1 mmto 1 mm., typically 0.25 mm.

Oblique Implant

Referring now to FIGS. 2A-2H, there is illustrated an oblique implant200. In some respects, an oblique implant 200 may resemble thejust-described PLIF implant 100. By analogy with other embodimentsdescribed herein, oblique implant 200 can have central opening orpassageway 206, polymeric component 210, recesses 212, trailing endcomponent 220, recesses 222, central hole 224, substantially-solidregion 226, porous region 228, protrusions 230, holes 232, pins 234,solid regions 250 and 252, porous region 254, and pins 256.

In oblique implant 200, polymeric component 210 may contain a pattern ofpeaks 260. The peaks 260 may be in the form of pyramids or truncatedpyramids. The peaks 260 may be configured in a pattern that is arectangular grid having principal axes that are generally orthogonal toeach other. In an oblique implant 200, it is possible that none of theprincipal axes of the grid pattern of the peaks 260 may be parallel toany principal axis of the overall oblique implant 200. Also, it ispossible that none of the principal axes of the grid pattern of thepeaks 260 may be perpendicular to any principal axis of the overalloblique implant 200 in the plane of the surface of the implant. This isillustrated in FIG. 2A.

As illustrated especially in FIG. 2B-2D, the implant 200 can have alordosis angle, i.e., if one views along the long horizontal directionof the implant 200, one of the walls is taller than the opposite wall.Also, as visible in such a view, the slope of the superior or inferiorsurface of one wall and the slope of the superior or inferior surface ofthe other wall may both be non-horizontal. Also, as visible in such aview, the slope of the superior or inferior surface of one wall can bedifferent from the slope of the superior or inferior surface of theother wall. As a result, the metal pad 249 on one side of the implant200 is shown as having a flat surface that is oriented differently fromthe corresponding flat surface of the metal pad 249 on the other side ofthe implant 200. Also, as illustrated, along the longer direction of thewalls, the implant 200 has some curvature of its bone-facing surfaces.

TLIF Implant

Referring now to FIG. 3A-3H, in an embodiment of the invention, theremay be provided an implant 300 comprising a polymeric component andmetallic components in the arrangement shown. Such device may besuitable for a TLIF surgical approach (Transforaminal Lumbar InterbodyFusion). In some respects, such an implant 300 may share certainfeatures with the already-described PLIF implant 100. In other respects,unlike the PLIF implant 100, the TLIF implant 300 may have an overallshape that is a generally-curved (banana) shape. Such an implant 300also may have certain specialized features regarding interface with aninstallation instrument, and may have certain other features relating toassembly of its components.

The TLIF implant 300 may have a central opening 306 therethrough along acephalad-caudal direction. The TLIF implant 300 may have an endcomponent 320 that may be metallic. The end component 320 may besuitable to join to polymeric component 310.

FIG. 3A shows the TLIF implant 300 including all of its componentsassembled to each other. FIG. 3B shows the polymeric component 310 only.In FIG. 3C, the polymeric component is omitted, and all other componentsare shown. By analogy with other embodiments described herein, TLIFimplant 300 can have central opening 306, polymeric component 310,recesses 312, trailing end component 320, recesses 322, central hole324, substantially-solid region 326, porous region 328, protrusion 330,hole 332, pin 334, solid regions 350 and 352, porous region 354, andpins 356.

The end component 320 may be suitable to be grasped by an installationinstrument (not illustrated). Furthermore, there may be providedengagement features 384 such as teeth near an upper surface and a lowersurface of the end component 320. The engagement features 384 such asteeth may be suitable to be engaged by a feature of an installationinstrument. The end component 320 may comprise a porous region and asubstantially-solid region. The porous region 328 of the end component320 may be bone-facing on both upper (cephalad) and lower (caudal)surfaces of the end component 320.

Furthermore, the end component 320 may have a protrusion 330 thatcooperates with the polymeric component 310 to participate in amechanical connection between the end component 320 and the polymericcomponent 310. The protrusion 330 may have a hole 332 therethroughgenerally along the cephalad-caudal direction of the implant 300. Thehole 326 may be suitable to receive a pin 334 in a press-fit situation.The protrusion 330 may be made of substantially-solid material, whichmay be continuous with substantially-solid material in other parts ofthe end component 320.

Near an end of the implant 300, there may be a defined post 380 that isa portion of a cylinder or prismatic solid, which may amount to morethan 180 degrees of external circumference of a cylinder or prismaticsolid. The shape of post 380 does not need to be circularly cylindricaleverywhere. For example, alternatively the post 380 could be a polygonalprism, or a combination of curved surfaces and prismatic planarsurfaces, with any of those shapes or combination of shapes beingextruded along the cephalad-caudal direction. The shape or extent ofpost 380 may be defined in part by a tool-accepting recess 312, 322 inthe exterior of the implant 300. The tool-accepting recess may begenerally located at or near the midplane of the implant 300. Thetool-accepting recess may exist partly (322) in the end component 320and partly (312) in the polymeric component 310. In FIG. 3G, it can beseen that the void space, which defines the post 380 for gripping by theinstallation instrument and creates more than 180 degrees of perimeterof the post 380, includes void space in the metallic end component 320and void space in the polymeric component 310. This allows achieving thedesired range of gripping of the post 380, while also achieving thedesired proportion of space allocated to the end component 320 and spaceallocated to the polymeric component 310. The post 380 may be partiallyin the region of end component 320, which may be metallic, and partiallyin the polymeric component 310.

The polymeric component 310 may have a protrusion-accepting hole 314,generally in a horizontal direction, suitable to accept the protrusion330 from the end component 320. The protrusion-accepting hole in thepolymeric component may be a through-hole and may have arounded-rectangle shape. In the polymeric component 310, there may be apin-accepting hole 332 that intersects the protrusion-accepting hole314. The pin 334 may have an interference fit relationship with respectto hole 332 in the protrusion 330, and may form a fit that is slightlylooser than an interference fit with respect to hole 332 in thepolymeric component 310. Alternatively, the opposite situation is alsopossible.

As can be seen in FIGS. 3B-3E, there may be a relationship between thepolymeric component 310 and end component 320 such that when polymericcomponent 310 and end component 320 are in their assembled relation toeach other, even if pin 334 is not present, there are constraints onpossible motion between polymeric component 310 and end component 320.As illustrated, when polymeric component 310 and end component 320 arein their assembled relation to each other, essentially the only degreeof freedom of motion that is permitted is translation along thedirection of the implant 300 that the axis of hole 314, which is adirection of motion that would cause shear of pin 334 if pin 334 were inplace. There is constraint against relative motion of the two partsalong the direction of pins 334. As a result of such constraint, it issufficient if pin 334 forms a press-fit in only one of the threeinteractions with components 310, 320; it is not necessary for apress-fit to exist between pin 334 and both polymeric component 310 andend component 320. For example, a press-fit might be created between pin334 and end component 320, while there is a looser fit relationshipbetween pin 334 and polymeric component 310 in either or both of thesuperior and inferior directions. Other fit relationships are alsopossible as long as there is one press-fit along the length of pin 334.Such provision of a press-fit relationship at less than all of theinterfaces of pin 334 may be helpful in reducing the amount of insertionforce that is needed to insert pin 334 (which is somewhat narrow andmight be susceptible to buckling).

As illustrated, the polymeric component 310 may have recesses suitableto accept metallic components such as pads 349. There may also beprovided metallic components such as pads 349, which may comprise bothsubstantially-solid regions 350, 352 and porous regions 354. Opposedmetallic components may be connected by a pin 356, which may have apress-fit engagement with the metallic components such as pads 349. Inpolymeric component 310 there also may be holes joining opposed suchrecesses, suitable to be occupied by pins 356. Such components andfeatures may be similar to components and features described elsewhereherein in connection with other geometries of implants. This embodimentof implant 300 may have a “barbell” construct as described elsewhereherein in connection with other embodiments.

As discussed elsewhere herein, the metallic components (such as endcomponent 320 and various pads 349) may protrude further toward the boneat the surgical site than the polymeric component 310, while thepolymeric component 310 may have a larger dimension of roughness thanthe metallic components.

The implant 300 may have an indexing feature 384 near post 380. Duringthe process of implantation of implant 300 at the surgical site, thepost 380 may be grasped by a grasping feature of the installationinstrument, and the indexing feature 384 may be interacted with by acorresponding feature of the installation instrument. The indexingfeature 384, in combination with its interaction with the installationinstrument, may be such as to define a number of discrete positions asrepresented by the angle between the implant 300 itself and the shaft ofthe installation tool. During the process of implanting such an implantat the surgical site, this angle may be changed as a result of actionstaken by the surgeon.

In such an implant, as illustrated, there may be provided a superiorindexing feature 384 superior of the region of post 380, and an inferiorindexing feature 384 inferior of the region of post 380. As illustrated,the indexing features 384 comprise teeth. As an alternative to teeth, itwould also be possible to provide other geometric indexing features atdesired angular locations. The superior and inferior indexing features384 are illustrated as being in vertical alignment with each other(along the cephalad-caudal direction of implant 300). The indexingfeatures 384, such as teeth, may be equally spaced with respect toangular position around the axis of post 380, but they do not have to beequally spaced.

In such an implant 300, the post 380 can be described by the shape ofits cross-section, which may be a cross-section taken in a plane that isperpendicular to the longitudinal or extruded shape of the post. Thelongitudinal or extruded direction of the post may correspond to thecephalad-caudal direction of the implant. The cross-sectional shape ofthe post 380 may be a polygon, which may be a regular (equal-sided)polygon. The polygon may have an even number of sides 386 so that thereare parallel sides that can be grasped in opposition to each other.Alternatively, grasping does not have to be by flat parallel surfacesagainst other flat parallel surfaces, but rather could involve anindented surface of the grasper contacting a corner of a polygonal shapeof the post 380, which may involve the grasper contacting both of thepolygon sides that meet to form the corner.

The polygon of post 380 may be a regular polygon. It is further possiblethat the polygon of post 380 might not be a regular polygon and theindexing features 384 such as teeth might not be equally-spaced either.In any such situation (either regular spacing or irregular spacing), theangular locations of the sides 386 of the polygon and the angulararrangement of the indexing features 384 may be coordinated such thatwhen the installation instrument is locked to set a particular angularposition with regard to the indexing features 384, a grasping feature ofthe installation instrument also is suitably positioned to optimallygrasp the post 380 such as polygonal sides 386 of the post 380. Therelationship between the installation instrument, the indexing featuresand the post 380 may be such that whenever the installation instrumentinteracts with the indexing feature to position the implant 300 in oneof the discrete positions permitted or encouraged by the indexingfeature, the grasping feature grasps features of post 380 in a desiredlocally-optimum manner of grasping. For example, a desired grasp of post380 could be a flat surface of the grasping feature in contact with acorresponding flat surface of the post 380. Or, a desired grasp of post380 could be a grasping surface having an indented shape that contacts acorner and the flats that join to make the corner. Grasping on one sideof the post could be either grasping of the flat geometry or graspingthe corner geometry, and grasping on an opposite side of the post 380could be either of the flat geometry or the corner geometry, in anycombination.

Furthermore, it is possible that with the engagement feature 384 (suchas teeth) having more than one permitted engagement position, there isan engagement angular interval between adjacent ones of the permittedpositions. It is further possible that on the post 380 the flats orcorners define a gripping angular interval between adjacent ones of theflats or the corners. It is further possible that the engagement angularinterval equals the gripping angular interval. In a related approach, itis possible that the gripping angular interval can be an integermultiple of the engagement angular interval, or the engagement angularinterval can be an integer multiple of the gripping angular interval.One way that gripping of a polygonal shape can be performed is by flatsof the gripper against flat surfaces of the polygon. It is also possiblethat an indented shape of the gripper can grip some combination ofcorners and flats.

As described elsewhere herein, the post 380 may be partly made of themetal of end component 320, and partly of polymer of polymeric component310.

Lateral Implant

Reference is now made to FIGS. 4A-4E, which illustrate an implant 400intended for insertion via a lateral surgical approach. FIGS. 4A-4B showthe assembled lateral implant 400. FIG. 4C shows the polymeric component410 of the lateral implant 400. FIG. 4D shows the non-polymericcomponents of the lateral implant 400. By analogy with other embodimentsdescribed herein, lateral implant 400 can have central passageway 406A,406B, polymeric component 410, recesses 412, trailing end component 420,recesses 422, central hole 424, substantially-solid region 426, porousregion 428, protrusions 430, holes 432, pins 434, pins 444, solidregions 450 and 452, and porous region 454.

In plan view, such an implant 400 may have a wall that proceeds aroundthe perimeter of the implant 400. Additionally, the implant 400 may havea ligament that connects a place on the wall with another opposed placeon the wall. In combination, the wall and the ligament may define twoopenings 406A, 406B through the implant 400. In plan view, such animplant 400 may be elongated such that it has an aspect ratio (overallexternal dimension in one horizontal dimension divided by overallexternal dimension in a second horizontal direction orthogonal to thefirst horizontal direction) that is greater than 2:1, or greater than3:1. If desired, for a highly elongated implant of this type, it wouldbe possible to provide three openings through the implant instead of theillustrated two openings 406A, 406B.

The lateral implant 400 may comprise a polymeric component 410, whichmay comprise PEEK or PEEK enhanced with particles of an osseointegrativematerial. The implant 400 may also comprise one or more metalliccomponents. The polymeric component 410 and the metallic component(s)may be arranged such that on the superior bone-facing surface of theimplant 400, progressing around the circumference, there may be asequence of polymeric surface, followed by metallic surface, and so onin an alternating progression. The same may be true for the inferiorbone-facing surface. The metallic components may be mechanically joinedto the polymeric component 410.

Some or all of the metallic components may comprise a region 450, 452that is solid or substantially-solid, and may further comprise a porousregion 454. The porous region 454 may be exposed to the exterior, i.e.,may be bone-facing.

The implant 400 further may comprise an end component 430 that maycomprise metal. The end component 430 may be solid or substantiallysolid, or it may have a substantially-solid region and a porous region.If a porous region 428 is present, it may have a bone-facing surface onthe exterior of the implant 400. End component 420 may have protrusions430 analogous to those in other implants. The implant 400 may be suchthat at the midplane, there is a continuous path of polymeric materialexcept that the end component 430 of the implant 400 may be metallic.

For a lateral implant 400 as illustrated, a lordosis angle may bedefined as the angle between a flat plane that is a generally flatsurface that is tangent to or parallel to the top surface of theimplant, and a generally flat surface that is tangent to or parallel tothe bottom surface of the implant As illustrated, the lateral implant400 exhibits some non-zero lordosis angle. This is visible in FIG. 4B.In FIG. 4B the difference in elevation between the metallic componentsand the adjacent polymeric component is also visible.

The lateral implant 400 as illustrated, has a longitudinal direction,between a first end and a second end. At a first end, which may besuitable to be grasped by an installation tool there may be a trailingend component 420. Trailing end component 420 may be all metal, althoughsome region of it may be substantially-solid metal 426 and anotherregion of it may be porous metal 428. The leading end, which is opposedto the trailing end, may comprise a superior bone-facing componentcomprising metal (which may comprise a substantially-solid region and aporous region), and an inferior bone-facing component comprising metal(which may comprise a substantially-solid region and a porous region),with the superior bone-facing component and the inferior bone-facingcomponent joined to each other by pins 444.

The lateral implant 400, as illustrated in FIG. 4E, has leading edgemetallic components. These may form a barbell construct with each other,analogous to those described herein for other implants. Intermediatealong the length of the implant 400 there also may be metallic pads 449on the superior surface and the inferior surface of the implant 400,which may be on the ligament that spans between the two long sides ofthe implant 400. The pads 449 may be joined to each other by pins 456 ina barbell construct analogous to those described herein for otherimplants.

Cervical Implant

Referring now to FIG. 5A-5I, in an embodiment of the invention, theremay be provided an implant 500 that may be suitable for use in fusion ofthe cervical spine. FIG. 5A shows an assembled cervical implant 400.FIG. 5B shows the polymeric component 510A, 510B of the cervical implant400. FIG. 5C shows the non-polymeric components of the cervical implant500. FIG. 5D shows the implant 400 exploded for ease of visualization.By analogy with other embodiments described herein, cervical implant 500can have central opening 506, polymeric component 510A, 510B, trailingend component 520A, leading end component 520B, recesses 522, centralhole 524, substantially-solid region 426, porous region 428, protrusions530, holes 532, and pins 534. The implant 500 may have a firstbone-facing surface and an opposed second bone-facing surface and acentral opening 506 therethrough from the first bone-facing surface tothe second bone-facing surface.

The implant 500 may comprise polymeric components 510A, 510B andmetallic components 520A, 520B in the arrangement shown. As illustrated,in sequence from front to back of the implant 500, there may be a firstmetallic component 520A, followed by polymeric components 510A, 510B onrespective sides, followed by a second metallic component 520B. Any ofthe metallic components may comprise a substantially-solid region 526and a porous region 528. The porous region 528, if present, may beexposed on an external surface that is a bone-facing surface withrespect to the position of the implant 500 when implanted in a patient.

As discussed elsewhere herein, the metallic components 520A, 520B mayprotrude further toward the bone than the polymeric components 510,while the polymeric components 510A, 520B may have a larger dimension ofroughness than the metallic components 520A, 520B. This is visible inFIG. 5E.

Mechanical connection between respective components may be made by a pin534 that may have a press-fit engagement with at least one of thecomponents.

FIGS. 5A-5E show a cervical implant 500 such that both the upper surfaceand the lower surface are generally planar, in an overall sense(disregarding localized features such as peaks and roughness and theslight offset between the metal surface and the adjacent polymericsurface). A generally flat surface that is tangent to or parallel to thetop surface of the implant, and a generally flat surface that is tangentto or parallel to the bottom surface of the implant, may form an anglewith each other. The angle is a lordotic angle, and the implant may betermed a lordotic cervical implant.

FIGS. 5F-5G show a cervical implant 500 that may be referred to as aconvex cervical implant. In this implant, just as in FIG. 5A-5E, thelower surface is generally planar, in an overall sense (disregardinglocalized features such as peaks and roughness and the slight offsetbetween the metal surface and the adjacent polymeric surface). On theother hand, for the upper surface, an enveloping surface that would belocally tangent to the upper surface at a size scale larger than theroughness may have a compound curvature, such that it is curved in eachof two directions that are orthogonal to each other. In FIGS. 5F-5G, theupper surface is convex in each of the two directions. Such an implant500 may still have an overall effective lordosis, but such lordoticangle would have to be defined specifically in terms of where a definingplane is tangent to the compound-curved surface. As illustrated, thelordotic angle of the convex implant of FIGS. 5F-5G is approximatelyequal to the lordotic angle of the lordotic implant illustrated in FIGS.5A-5E.

Referring now to FIGS. 5H-5I, in regard to the porous region, thethickness (in the cephalad-caudal direction) of the porous region 528does not have to be uniform across the extent of the metallic componentin directions that are perpendicular to the cephalad-caudal direction,such as the lateral direction. Some examples of this occur in thecervical implant 500.

Referring now to FIG. 5H, the device may have a feature such that, inone of the metallic components, the porous region 528 has a thickness,measured in a direction that is perpendicular to a bone-facing surfaceof the porous region, such that the thickness is tapered in a directionfrom the first side polymeric component toward the second side polymericcomponent. At the posterior of the cervical implant 500, the porousregion tapers toward each side of the implant 500, as a way of providinga gradual transition of properties and strength.

Referring now to FIG. 5I, the device may have a feature such that, inone of the metallic components, the porous region 528 has a thickness,measured in a direction that is perpendicular to a bone-facing surfaceof said porous region, wherein the thickness varies to accommodate afeature such as an instrument interface hole. At the anterior of thecervical implant 500, it is illustrated that the porous region isslightly thinner in the region of the instrument interface (draw-rod)hole, compared to its thickness in other places. This providesadditional strength by in the vicinity of the draw-rod hole, byproviding additional substantially-solid material in that vicinity.

ALIF Implant

Referring now to FIGS. 6A-6F, there is illustrated an implant 600 thatcould be used in an ALIF (Anterior Lumbar Interbody Fusion) procedure.The implant can comprise a polymeric component 610 and a metalliccomponent 620 that are partially interleaved with each other. Themetallic component 620 can have essentially a slot, into which a portionof the polymeric component 610 may fit. This may be thought of as a“hand-in-glove” configuration. The metallic component 620 and thepolymeric component 610 can be interleaved such that at the anterior(trailing) edge the implant 600 is entirely metallic, and at theposterior (leading) edge the implant external surface is entirelypolymeric, and at the interior of the central opening 606, the perimeteris entirely metallic at the superior surface and entirely metallic atthe inferior surface but at the midplane the interior of the centralopening 606 is a series of metallic and polymeric and metallic.

In an embodiment, there may be a ring 642 of metal going entirely aroundthe perimeter of the device on the interior of the ring 642 at a firstbone-facing surface, and there may be a ring 642 of metal going entirelyaround the perimeter of the tubular device on the interior of the ring642 at a second bone-facing surface, and at the midplane there may bemetal on only a portion of the interior of the ring 642. On the exteriorof the ring 642, the exterior surface of the device may have exposedpolymer on a majority of the exterior of the device.

In an embodiment, a majority of the sideways exterior side surfaces ofthe implant 600 may be polymeric, and on the interior of the centralopening 606, there may be continuous metal all the way around theinterior perimeter at one bone-facing surface and at a second opposedbone-facing surface but not at the midplane of the implant 600.

In an embodiment of the invention, the implant 600 may have acombination of components such that along the anterior-posteriordirection, there is a series of materials in the order metal(anteriorly) followed by polymer followed by metal (posteriorly).

In an embodiment of the invention, the implant 600 may have acombination of components such that along the anterior-posteriordirection, there is a series of materials in the order metal(anteriorly) followed by polymer followed by metal (posteriorly). Themetallic component 620 can be subdivided into a substantially-solidregion 626 and a porous region 628.

In the illustrated embodiment, the metallic surface may be moreprotruding toward bone than is the surface of polymeric component 610.The surface of polymeric component 610 may have engagement features 660such as pyramids or sharp or pointed features such as to preventexpulsion of the implant 600. The engagement features 660 may havedimensions that are larger than the dimensions of any porosity orroughness that may be present on bone-facing surfaces of the metalliccomponent 620, such as substantially-solid region 626 and a porousregion 628. As illustrated, on the bone-facing surface, where metal isadjacent to polymer, the polymer is closer to the central opening orpassageway 606 than is metal.

In the illustrated embodiment, the metallic component 620 may have somesubstantially-solid region 626, and some porous region 628. The metalliccomponent 620 and the polymeric component 610 may be joined to eachother by a pin 644 in a press-fit condition. In such a situation, forcompression in the cephalad-caudal direction, the overall modulus ofmuch of the implant may be similar to the modulus of natural bone,because the modulus of PEEK more closely resembles the modulus ofnatural bone than does the modulus of solid titanium.

In ALIF implant 600, it is provided that in metallic component 620, theporous region 628 extends to the edge of metallic component 620 wherethe metallic component 620 borders on central opening 606. It isbelieved that this feature provides encouragement for bone at thecontacting vertebra endplate surface, to enter the porous region 628,and to continue to grow into the interior region or central opening 606of implant 600. In spinal fusion surgery, it is typical to place bonechips and growth-promoting substances of various sorts in centralopening 606 to encourage bone to grow in and form a continuous bonystructure from one vertebra to the next vertebra. In somewhat moredetail, it is illustrated that, of the four sides of the implant 600,facing central opening 606, this porous edge occurs on three sides (theanterior and two lateral sides). On the other hand, the edge at theposterior is illustrated as being substantially solid metal, whichprovides additional strength at that location.

As illustrated, implant 600 also has a pin 656 that may be press-fittedinto metallic component 620 at both or at least one of its ends. The pin656 may anchor polymeric component 610 in assembly with metalliccomponent 620.

Further Details about Press Fits

Mechanical fits are described in references such as ANSI B4.1 standard,in regard to dimensions of parts and also tolerances on thosedimensions. A pin or shaft or cylindrical object may be described,including its tolerance, so as to have a maximum permissible outsidediameter and a minimum permissible outside diameter. Similarly, a holemay be described as having a maximum permissible inside diameter and aminimum permissible inside diameter. A slip fit is when any combinationof permissible inside diameter and permissible outside diameter has agap between the hole and the cylindrical object. An interference fit iswhen any combination of permissible inside diameter and permissibleoutside diameter has interference between the hole and the cylindricalobject. A transition regime is when some combinations of permissibleinside diameter and permissible outside diameter have a slip fit whileother combinations of permissible inside diameter and permissibleoutside diameter have an interference fit. In embodiments of theinvention, dimensions and tolerances may be chosen to result in anappropriate amount of interference such that at the loosest conditionthere is an interference fit sufficient to keep the parts together asdesired, and the tightest condition, which is also an interference fit,the fit is still easy enough to assemble. For example, it is believedthat for nominal diameter of 0.031 inch, and what may be described as alight drive fit (F1), appropriate dimensions for the pin may be0.0315/0.0313 inch, and appropriate dimensions for the hole may be0.03125/0.03100 inch. This results in an interference that can rangefrom 0.0005 inch to 0.00005 inch depending on the combination ofpermitted diametral dimensions. However, it is not wished to be limitedto these dimensions. It would also be possible to use a medium drive fit(F2) or other fit as desired. Furthermore, for example, when one of thecomponents of the interference fit has a modulus of elasticity that isdifferent from the modulus of elasticity of the other component, someadjustment to such ranges of dimensions may be appropriate.

When two components are mechanically joined to each other, suchmechanical joint can be a pinned joint in which a pin such as acylindrical pin extends through both components and isinterference-fitted or press-fitted into at least one of the components.As illustrated, such pins may be oriented in a generally caudal-cephaladdirection, although other directions are also possible.

A press-fit condition can be achieved, as in known machine shoppractice, by providing a known, small amount of dimensional interferencebetween parts that are intended to mate with each other, such as a dowelpin and a hole. Because of close tolerances required on both the pin andthe hole, the dowel pin is typically finish-manufactured by a grindingoperation and the hole is typically finished by a reaming operation. Fordiameters of current interest, which are in the range of 1 mm, theinterference (overlap in diameters of the pin and the hole when each ofthose components is measured in a separated condition) is describedherein. A press-fit is often used with parts that are metal. Insituations of interest to the current application, it may be desirablethat the pin be made of metal and, where a hole for press-fit isprovided, that hole be provided in metal that is substantially solid(rather than the porous region described herein). The press-fit wouldmost commonly be a cylindrical pin engaging with a cylindrical hole,although other shapes and geometries are also possible.

In a situation in which a press-fit pin passes successively throughthree different components or regions or materials along the length ofthe pin, it is possible that a press-fit condition could exist in allthree places. However, it is also possible that the assembly could holdtogether satisfactorily if a press-fit condition exists at less than allthree places. For example, it might be sufficient if a press-fitcondition only exists at two out of the three places, such as apress-fit existing at one end of the press-fit pin and at the other endof the press-fit pin, while a somewhat looser condition might existaround the middle of the press-fit pin. This situation can occur in FIG.1F. For some designs involving three regions of contact with one pin, itwould be possible that only one of the regions of contact might be apress-fit, and the assembly would still hold together. This situationcan occur in FIGS. 3C, 4D. It is possible that the pin could have apress-fit relationship with the hole in the body, or, alternatively, thepin could have a relationship with the hole in the body that is lesstight than a press-fit. In the TLIF design illustrated herein, there isa press-fit pin passing through three layers of materials that could beadequately constrained by press-fitting in only one of the three layersof materials, i.e., the central layer. It is also possible that the fitbetween some of the components could be a tight press-fit and the fitbetween other components could be a lighter press-fit or a sliding fit.All of this can be accomplished by appropriate dimensions andtolerancing. In general, any combination of tightness of press-fit orlooser form of fit may be provided.

In situations where a pin exists in two different materials, it ispossible that press-fit in only one of those two materials issufficient. For example, in the PLIF design illustrated herein, wherethe end component joins to the polymeric component in two distinctplaces one upper and the other lower, it is sufficient if press-fitcondition exists only one of the two places, such as at the pin-to-metalinterface.

In the “barbell” designs illustrated herein, the holes in both metalliccomponents could be through-holes, or the hole in one of the metalliccomponents could be a blind hole while the hole in the other of themetallic components could be a through-hole, or it is even possible thatthe holes in both metallic components could be blind holes. To createthe press-fit, the pin may have dimensional interference with thecorresponding hole in each of the metallic components.

In a metallic component that receives a press-fit pin and contains botha porous region and a solid region, if the press-fit hole goes throughthe bone-facing surface, there may be provided a region of thebone-facing surface that is solid or substantially-solid in the vicinityof the press-fit. Alternatively, if the hole for the press-fit with thepin is a blind hole, the entire bone-facing surface of the metalliccomponent, or the bone-facing surface that is in line with the pin, maybe porous. In such a situation, away from the bone-facing surface theremay be provided a solid or substantially-solid region in which thepress-fit occurs. As yet another alternative, it would be possible toprovide a press-fit hole that extends through both thesubstantially-solid region and the porous region. In such a situationthe press-fit with the pin in the porous region might not be as tight asthe press-fit with the pin in the substantially-solid region, but stillthere would be a press-fit in some places to accomplish the desiredassembly.

It is illustrated that the exterior-facing surface of pad 149 comprisessome porous metal, and also comprises substantially-solid metal thatsurrounds the pin 156 and participates in a press-fit. It is alsoillustrated that the interior-facing surface of a pad such as pad 149comprises entirely substantially-solid metal. It is also possible thatthe interior-facing surface of pad such as pad 149 may comprise lessthan all but still a majority of substantially solid metal withoutactually being entirely substantially-solid metal. As illustrated, theexterior-facing surface of pad such as pad 149 may have a majority ofporous metal and a minority of its surface represented by the exposedsubstantially-solid metal together with the pin.

In various places in implant 100, different press-fit geometries exist.Some of the press-fits are “barbell” constructs, and so in order for theimplant to remain assembled, it is necessary for all of themetal-to-metal press-fits to remain tight. With a “barbell,” it is lessimportant what kind of fit there is between the pin and the polymericcomponent, as long as the pin is not allowed to buckle duringpress-fitting. In fact, for that situation, less friction between thepin and polymeric component might be preferable because if there is anupper practical limit to the amount of insertion force that can beapplied to the pin, such a distribution of fits and tolerances wouldallow a larger proportion of that insertion force to be used forcreating the final metal-to-metal press-fit during assembly. In contrastto this situation, there is also another type of situation that involvescapturing of one part in another part. In some situations, in additionto press-fitting of a pin, there is also a geometric capturingrelationship where the metal end piece joins the PEEK body, and so evenif one of the fits (the fit of the pin in the polymeric component or thefit of the pin in the metal) is loose, the other press-fit will keep theimplant together successfully. In such a situation it would be possibleto have the pin/polymer fit being loose and pin/metal fit being tight,or to have the pin/polymer fit being tight and the pin/metal fit beingloose. (Of course, it is also possible that both fits could be tight). Acapturing relationship could exist where an overall feature of themetallic component slides into a corresponding feature of the polymericcomponent or vice versa. Such a relationship could constrain relativemotion between the two components in some directions but allow motionalong the direction of insertion for coupling the two components. Then,a press-fit pin could further constrain and couple the two components.

It would also be possible, if desired, to provide some form ofsupplemental fixation in addition to the described press-fit involvingthe pin. For example, after assembly, a pin could be spot-welded to itsneighboring metallic component. It would also be possible to plasticallydeform a localized region of the pin or of one of the metalliccomponents that is in contact with the pin. It is possible that when apin is shortened after press-fitting, that cutting operation could beperformed in such a way as to leave a burr or similar feature thatcontributes to locking. It would also be possible that one of themetallic components has a metallic component polymer-facing sidesurface, and the polymeric component has a corresponding polymericcomponent metal-facing side surface, and there could be an interferencefit between the metallic component polymer-facing external side surfaceand the polymeric component metal-facing side surface.

Method of Assembly

Embodiments of the invention may comprise a method of assembly.

It can be noted that, especially in configurations such as the “barbell”configuration, the pin involved in press-fit may be somewhat long andslender. If compressive force needs to be applied to the pin to forcethe pin into press-fit engagement with a metallic component, and if theforce is applied at the pin end opposite from the press-fit, and if thepin were unconstrained over much of its length, it is possible that thepin could be vulnerable to buckling. Therefore, a possible assemblysequence is described here. Initially, the pin and one metalliccomponent such as pad 149 could be urged into press-fit engagement witheach other, in isolation from any other components of the implant. Thisengagement process could be performed with the pin being held in a chuckor similar tooling that grasps much of the length of the pin, or withthe pin being provided with some form of close but slightly loosesideways constraint or support such as a close-fitting but slightlyloose hole. Such support or constraint could prevent buckling of the pinduring this step of the assembly. Then, the pin (such as 156, 256, 356,456) can be inserted into the hole in the polymeric member (110, 210,310, 410, 510). The hole in the polymeric member can be sufficientlyloose with respect to the pin that there is no risk of causing the pinto buckle as the pin is inserted into the hole. Finally, the pin can beurged into engagement with the second metallic component by applicationof opposed compressive forces to the two metallic components. While thisapplication of force is occurring, the hole in the polymeric member canprovide sideways support to the pin to prevent the pin from bucklingduring application of insertion force. The polymeric member and the pincould have a sliding fit with respect to each other, or could be atransitional fit (which might be either sliding or interferencedepending on the stack-up of tolerances in an individual situation), orthe fit in the polymeric component could be a press-fit but looser thanthe press-fit in the metallic component). Alternatively, the pin couldfirst be inserted into the hole in the polymeric part, and then the twopads could be press-fitted onto respective ends of the pin. Otherassembly sequences are also possible.

This principle can also be used in other situations. For example, in theTLIF implant 300, a pin (such as 334) may pass through a polymericcomponent 310 and a metallic component and polymeric component 310. Thepin 334 may be inserted first through the polymeric component 310, whichmay have a looser-than-press-fit relationship with the pin, and then maybe forced through the metallic component in a press-fit relationship.During this step, the extending part of the pin 334 may be grasped in aheld in a chuck or similar tooling that grasps much of the length of thepin and urges the pin into its press-fit. The chuck can be repositionedas needed. During this process, the hole in the polymeric piece 310 canprovide support to prevent the pin from buckling. Then, the pin 334 canbe urged further in so that the pin 334 extends beyond the metalliccomponent into the polymeric component 310, where the fit can again belooser than a press fit. If the fit between the pin 334 and thepolymeric component is slightly looser than a press fit, that can reduceunnecessary exertion of force onto the pin 334 while still allowing thenecessary exertion of force for achieving press-fit where needed.

It is possible that at the time of installing the pin (such as 156, 256,356, 456, 656) and making the press-fit, the pin may be longer than theeventual pin in the completed implant (100, 200, 300, 400, 500, 600).Such extra length of the pin may, for example, be useful for thegrasping of the pin by a chuck or other tooling used during certainsteps of the assembly process. The excess length of the pin may beremoved at an appropriate time in the later part of the assemblyprocess, such as by a machining operation or other operation.

Yet another possibility is that a pin can be press-fitted into a blindhole (in contrast to a through-hole) in a metallic component.

Manufacturing Sequence

Described here is a possible manufacturing sequence for embodiments ofthe invention. It can be understood that described steps can be omittedor changed or re-sequenced if appropriate for a particular situation.Polymeric components can be manufactured by molding or machining or acombination thereof. In regard to metallic components, a first step canbe to manufacture, by additive manufacturing techniques, an early-stagemetallic component. For metallic components, the process may start witha powder of metal particles, such as particles of titanium or a titaniumalloy. The particles may be joined to each other or merged with eachother by application of energy such as by laser melting or lasersintering or by electron beam. It might also be possible, in selectedapplications, to use a three-dimensional printing process involving abinder fluid applied to the powder bed in selected places. Themanufacturing process may be controlled by software instructions thatmay be unique to a particular design. Such early-stage part can containboth substantially-solid regions and porous regions, as may be dictatedby the design of the part and as may be controlled by softwareinstructions governing the manufacturing process.

After the early-stage part is retrieved from the additive manufacturingprocess, machining operations can be performed if desired. Suchmachining may be performed primarily or entirely on portions of theearly-stage part that are substantially solid. Features that are holesin the finished product do not need to be manufactured as holes in theearly-stage part. For such features, the early-stage part can besubstantially solid in the relevant region and holes can be drilled inthe substantially solid material during the machining process. Thisincludes holes intended to be occupied by pins for press-fits. For suchholes, the early-stage part can be additively manufactured assubstantially-solid material in the appropriate place, and afterward ahole can be drilled through the substantially-solid material, and afterthat drilling, the drilled hole can be reamed to achieve the final holedimension with required accuracy. There may be other holes, not involvedin press-fits, that may be drilled in substantially-solid materialwithout being reamed afterward. There may be holes that are intended tobe internally threaded, such as for interface with a draw-rod. For suchholes, the early-stage part can be additively manufactured assubstantially-solid material in the appropriate place, and afterward ahole can be drilled through the substantially-solid material, and afterthat the drilled hole can be tapped to create the internal threads.

When working with the early stage part, it is also possible to usemachining operations to create certain surfaces, such as flat surfaces,on the part. For example, there may be flat surfaces that are involvedin the interface of the metal component with the polymeric component.This may occur at protrusions from the metal component that interactwith corresponding features of the polymeric component. Protrusions suchas protrusions 130, 230, 330 can be machined on their side surfaces.Such side surfaces, which may interact with corresponding machinedsurfaces of polymeric part 110, 210, 310, can be involved in thetrapping or other spatial relationship described elsewhere herein. Thedimensions and surface condition of machined surfaces can be moreprecisely controlled than the dimensions and surface condition ofsurfaces as they result from the additive manufacturing process. Flatsurfaces on the substantially-solid portions of pads 149 could bemachined if desired although they do not have to be. Exterior-facingsurfaces of metallic components do not have to be machined.

After machining, a part can be anodized if desired, such as to providedesired surface treatment or properties or to provide desired colors.

After that, the implant can be assembled, such as to join metalcomponents together with the polymeric component. This can includeperforming press-fits as appropriate.

After that, the assembled implant can be sterilized with, if necessary,the implant being enclosed in a pouch. Any of various appropriatesterilization procedures can be used, as known in the industry. Ifsterilization by heat is used, it may be appropriate to eliminate thepossibility of liquid water entering and remaining in crevices or poresof the implant. For example, dry heat sterilization can be used. Ifsteam sterilization is used, it is possible to use cycles that includeextended drying time at temperature, to ensure the evaporation of allliquid water.

For a surgical procedure, it is possible to provide a variety of sizesof implants, which may also include a variety of lordosis angles incombination with a variety of sizes of implants. Appropriateinstallation instruments can also be provided.

Anatomy

FIGS. 7A-7E illustrate various of the described implants in relation tovertebrae near which they would be implanted.

In the illustrated vertebrae, in the body of the vertebra that normallyadjoins the spinal disc (not illustrated), the body of the vertebra hasan internal structure, similar to other bones. In general, the outer ormore external region of a vertebral body contains relatively strongerand denser bone. The outer, harder denser bone is referred to as theapophyseal ring. In contrast, the interior region of a vertebral bodycontains bone that is less dense and softer and weaker. In somevertebrae such as the cervical spine, on the surface or endplate of thevertebral body facing the spinal disc or the implant, there is a concavesurface of the bone.

Referring now to FIG. 7A, implant 100 may be implanted as a pair ofimplants 100 in a spinal disc space. FIG. 7A illustrates a pair of PLIFimplants 100 in relation to a lumbar vertebra near which they may beimplanted. As illustrated, the outwardly-located (laterally-located)metal components located in the most extreme anatomically laterallocations are in contact with the apophyseal ring, thereby achievingstrong bony fixation with the strongest bone of the vertebral endplate.As illustrated, the metal components located more anatomically mediallyare in contact with the concavity of the vertebra thereby improvingfriction between the implant and bone. The metallic components achievecontact with the vertebrae at the time of implantation. The polymericcomponents 110 may achieve contact with the vertebrae upon settling(subsidence) or application of compressive load along the spine.

Referring now to FIG. 7B, there is illustrated a TLIF implant 300 inrelation to a lumbar vertebra near which it may be implanted. With theTLIF implant 300, one of the long curved sides of the implant 300 (theside that is placed more anteriorly) is in contact with the apophysealring. That long curved side comprises some polymeric surface and somemetal surface. The other long curved side of the implant 300 (which alsocomprises some polymeric surface and some metal surface), is in contactwith less-dense bone. The more anteriorly (anatomical direction) locatedmetal component, which is in contact with the apophyseal ring, mayachieve strong bony fixation. The more posteriorly (anatomicaldirection) located metal component may be in contact with the concavityof the vertebral endplate, thereby achieving good friction. Thepolymeric component 310 achieves contact with the vertebrae uponsettling or application of compressive load along the spine.

Referring now to FIG. 7C, in regard to lateral implant 400, the lateralsides of the implant 400, which have metal surfaces of end component 420and pad 449 at an end of implant 400 that is opposite end component 420,are in contact with bone of the apophyseal ring. FIG. 7C illustrates alateral implant 400 in relation to a lumbar vertebra near which it maybe implanted. Sets of metallic components 420 at theinstrument-interface trailing end component 420 contact the apophysealring. Sets of metallic components such as pads 149 at the leading endopposite the end component 420 also contact the apophyseal ring. A setof metallic components 450 in the middle of the lateral implant 400 maycontact the center on the concavity in the vertebral plate, which maymaximize bony contact/friction.

Referring now to FIG. 7D, FIG. 7D illustrates a cervical implant 500 inrelation to a cervical vertebra near which it may be implanted. Thebone-facing surface of the implant 600 may generally be in contact withthe apophyseal ring of the vertebral body.

FIG. 7E illustrates an ALIF implant 600 in relation to a lumbar vertebranear which it may be implanted. The perimeter of the ALIF implant 600may roughly correspond to the apophyseal ring. The bone-facing surfaceof the implant 600 may generally be in contact with the apophyseal ring,while the concavity of the vertebral plate may be in contact with bonegraft material in the central opening 606.

With spinal implants in general, it can be desirable that portions ofthe implant be radiolucent as a way of allowing long-term monitoring ofbone ingrowth by X-ray or other forms of radiography. PEEK isradiolucent, while metal such as titanium blocks X-rays. In embodimentsof the invention, in certain directions, there are provided certainline-of-sight views that are entirely through polymer with no presenceof metal. For example, with PLIF implants 100, anatomically lateralviews through some portion of the implant (or pair of implants) passentirely through polymer. Similarly, for oblique implant 200, there arecertain directions of view that pass entirely through polymer. For TLIFimplants 300, anatomically Anterior-Posterior views through some portionof the implant pass entirely through polymer. With Lateral implant 400,anatomically Anterior-Posterior views through some portion of theimplant 400 pass entirely through polymer. With Cervical implant 500,anatomically lateral views through some portion of the implant 500 passentirely through polymer. In ALIF implant 600, at the midplane of theimplant 600 (midway between the superior surface and the inferiorsurface), for much of the anatomically anterior-posterior dimension ofimplant 600, in an anatomically lateral view, there is a layer entirelyof polymer and a view or line of sight that passes entirely throughpolymer.

It also can be seen that in most of the embodiments of the invention,the end component 120, 220, 320, 420, 520, 620 is metallic for reasonssuch as interface with installation instrument, while much of the restof the implant is polymeric component 110, 210, 310,410, 510A, 510B,610. Therefore, for at least a majority of the bone-interfacing surfaceof the implant, the load path for compressive load in the verticaldirection passes through polymeric material with the exception of endcomponents 120, 220, 320, 420, 520A, 520B, 620 (and, in the case of theCervical implant 500, an additional exception at the posterior of thatimplant). In general, including some polymer in the load path isdesirable because the elastic modulus of the polymer is a better matchto the modulus of bone than is the elastic modulus of titanium orsimilar metals. This helps to avoid the problem of stress-shielding.

ALIF Implant with Anchoring Screws

Referring now to FIGS. 8A and 8B, there is illustrated an implant 800that can be used in an ALIF (Anterior Lumbar Interbody Fusion) procedureor other spinal fusion procedures. In an embodiment of the invention,the implant 800 may have a first bone-facing surface 804A and an opposedsecond bone-facing surface 804B, and may have a central opening 808extending from the first bone-facing surface 804A to the secondbone-facing surface 804B.

In an embodiment, the implant 800 may generally be considered tocomprise an anterior component 810 and a remainder of the implant 800,with the anterior component 810 and the remainder of the implant 800being mechanically joined to each other. In an embodiment, the anteriorcomponent 810 may be made of substantially-solid metal, such as titaniumor a titanium alloy, and the remainder of the implant 800 may be made ofor may comprise a polymeric material.

FIG. 8A shows the anterior component 810 assembled with the remainder ofimplant 800, while FIG. 8B shows the parts exploded away from eachother.

In embodiments of the invention, the remainder of the implant 800 maycomprise polymeric component 840. Polymeric component 840 may contain,embedded in the polymeric material, a radiopaque marker 848, which may,for example, comprise tantalum and may be in the form of a sphere orcylinder.

In an embodiment, the anterior component 810 may have a full-heightregion that extends fully from one bone-facing surface to the opposedbone-facing surface at least some of which comprises solid metal. Theanterior component 810 may also have a split or fork, posteriorly-facingas illustrated. The split or fork formed in anterior component 810 maycomprise a first extension 812 projecting, posteriorly as illustrated,from the anterior component 810 along a superior surface of the implant800, and a second extension 814 projecting, posteriorly as illustrated,from the anterior component 810 along an inferior surface of the implant800. The space between first extension 812 and second extension 814 maydefine a space therebetween that is suitable to receive a portion of thepolymeric component 840 or remainder of the implant 800.

Holes for Anchoring Screws

In an embodiment, the anterior component 810 may comprise one or moreanchoring screw holes 820 therethrough. Referring now to FIGS. 8C-8K,two such holes are illustrated. One end of the anchoring screw hole 820may pass through the anterior surface of the anterior component 810. Theother end of the anchoring screw hole 820 may exit partially through thebone-facing surface 804A or 804B of the implant 800. If the implant 800has two such anchoring screw holes 820, one anchoring screw hole 820Amay pass partially through the superior bone-facing surface 804A and theother anchoring screw hole 820B may pass partially through the inferiorbone-facing surface 804B.

In an embodiment, the anchoring screw holes 820A, 820B may be suitableto receive anchoring screws 828A, 828B therein. The anchoring screws828A, 828B may be suitable to engage with inferior or superior vertebraefor providing anchorage to those neighboring vertebrae, in a surgicalstrategy that is sometimes referred to as “stand-alone.” With respect toa lateral direction of the implant 800, the two anchoring screw holes820A, 820B may be located on opposite sides of the vertical midplane ofimplant 800 from each other, and may be symmetrically located at equaldistances from the vertical midplane of the implant 800.

In an embodiment, the anchoring screw holes 820A, 820B may be of largercross-sectional dimension at the anterior surface of the anteriorcomponent 810, and of smaller cross-sectional dimension where theanchoring screw holes 820A, 820B partially pass through bone-facingsurfaces 804A, 804B. The anchoring screw 828A, 828B may be able to enterthrough the anterior surface of the anterior component 810 but the headof the anchoring screw 828A, 828B may be unable to pass all the waythrough the anchoring screw hole 820A, 820B.

FIG. 8C shows a view of the anterior component 810 viewed from theposterior. Visible in FIG. 8C are two through-holes 820A, 820B suitableto receive anchoring screws 828A, 828B. FIGS. 8D-8G show variouscross-sections of anterior component 810. In FIGS. 8D and 8E, thecutting plane is a generally vertical plane and cuts through a smallligament that completes the perimeter of the socket that receives thehead of anchoring screw 820.

The direction of the axis of respective anchoring screw holes 820A, 820Bmay be at an angle that is somewhere between anterior-posterior andcephalad-caudal (superior-inferior) directions. As illustrated, theangle may be approximately 45 degrees with respect to the horizontalmidplane of the implant 800. As illustrated, one such angled anchoringscrew hole 820A is provided pointing superiorly and located on one sideof the center of the implant 800, and another such angled anchoringscrew hole 820B is provided pointing inferiorly and located on the otherside of the center of the implant 800.

In an embodiment, in the anterior component 810, the portions (or atleast most of them) immediately surrounding the anchoring screw holes820A, 820B may be substantially solid metal. In particular, the portions(which may be referred to as ligaments) directly above the anchoringscrew hole(s) 820A, 820B and directly below the anchoring screw hole(s)820A, 820B may be substantially solid metal. If there are two suchanchoring screws 828A, 828B, the portion of the anterior component 810that is located between the anchoring screw holes 820A, 820B also may besubstantially solid metal. In an embodiment of the invention, thelocations of solid metal and of porous metal may be configured such thatall of the material that is exposed at the internal surfaces of theanchoring screw hole 820A, 820B that contact or are near the region ofthe head of the screw 828A, 828B is substantially-solid metal. In anembodiment of the invention, if that is not achieved, at least 90% ofthe interior surface of the anchoring screw hole 820A, 820B may besubstantially-solid metal.

In an embodiment of the invention, the angled anchoring screw holes820A, 820B may have an internal surface. Some of the internal surfacemay comprise a portion of a sphere or, more generally, a concave curvedshape. Portions of the anchoring screw hole 820A, 820B closer to thebone-facing surface may be dimensioned so that a desired degree ofangulation of the shaft of anchoring screw 828A, 828B, within a definedrange of angles, is available, but angulation beyond such limits is notpermitted, due to contact between the shaft and edges of the anchoringscrew holes 820A, 820B.

The head of the anchoring screw 828A, 828B may have a spherical surfacethat is complementary to the internal surface of the hole 820A, 820B.The head of the screw 828A, 828B may bear against some of the internalsurface of the hole 820A, 820B, being rotatable with respect theretoaround various axes of rotation. This combination may allow a degree ofvariation of the angle at which the screw points. Such a screw can bereferred to as a polyaxial screw. Such a relationship results in theanchoring screw 828A, 828B being able to occupy a plurality of angleswith respect to the implant 800. The shaft of screw 828A, 828B mayinteract, for certain positions, with edges of anterior component 810near where the shaft of screw 828A, 828B joins the head of screw 828A,828B. Such interaction may define limits of angulation of screw 828A,828B. Taken together, such variability of angular position may allow theanchoring screw 828A, 828B to be positioned appropriately for anatomicalfeatures of a particular patient or a particular surgical site.

FIG. 8H shows an assembly of implant 800 with two anchoring screws 828A,828B. An individual screw 828A, 828B is shown in FIG. 8I, and itscross-section is shown in FIG. 8J. As shown in FIG. 8J, the head ofanchoring screw 828A, 828B may have an engagement feature such as aTORX® engagement feature, for engaging with a driving tool.Additionally, the head of anchoring screw 820A, 820B may have internalthreads for engagement with a draw-rod of an installation instrument.Although two such screws 828A, 828B have been illustrated in variousFigures, it can be understood that other numbers of screws are alsopossible.

In an embodiment of the invention, the location of substantially-solidportions of the anterior component 810 may be such that all, or almostall (such as greater than 90%), of the internal surfaces of theanchoring screw hole 820A, 820B are substantially-solid metal, asdescribed elsewhere herein.

Configuration of Substantially-Solid Metal and Porous Metal

As described elsewhere herein, it is possible to produce metalcomponents in which some portion is substantially-solid metal andanother portion is porous metal. Such combination may, for example, beproduced by additive manufacturing such as by providing metal powder andusing selective laser sintering or electron beam sintering to joinpowder particles to each other. The porous metal portion may be usefulfor promoting bone ingrowth, and the substantially-solid metal portionmay be useful for structural strength or other reasons.

The porous metal region, as illustrated, may exist in the full-heightportion of the anterior component 810 and may further exist in theextensions 812, 814 which is the split portion of the anterior component810. Any combination of such existence of porous regions is possible.Both the superior bone-facing surface 804A and the inferior bone-facingsurface 804B may have such porous portion. The configurations of porousmetal and substantially solid metal may be identical on the superiorbone-facing surface 804A and the inferior bone-facing surface 804B, orthey may be different.

The porous regions 818A, 818B, 818C, 818D may extend into the metalliccomponent 810 (along the superior-inferior direction) to a defineddepth. Such depth is illustrated as being generally a constant depth.This is visible in FIG. 8L, in which the porous regions 818A, 818B,818C, 818D are shown exploded away from the solid metallic region 816.More generally, such depth may vary as a function of position on thebone-facing surface 804A, 804B.

In an embodiment, bone-facing surfaces 804A, 804B of the anteriorcomponent 810 may comprise some regions of porous metal. In anembodiment, the bone-facing surface 804A, 804B may comprise porousregions 818A, 818B, 818C, 818D. These porous regions 818A, 818B, 818C,818D may be located in places that are lateral (more exteriorly oroutwardly with respect to the vertical midplane) of the respectivecenterlines of anchoring screw holes 820A, 820B. In an embodiment, aboundary of the central opening 808 may comprise a straight-line segmentin a generally anterior-posterior direction, and all of the porous metalregion 818A, 818B, 818C, 818D may be located outboard, in a lateraldirection, of the respective straight-line segment. In embodiments, allof the porous metal regions 818A, 818B, 818C, 818D may be locatedlaterally outboard of the central opening 808.

Possible location of porous metal regions 818A, 818B, 818C, 818D isfurther illustrated in FIG. 8M. In an embodiment, a parallel-boundedregion may be defined by two planes 844A, 844B that are parallel to eachother and are parallel to the longitudinal axis of the implant 800. Thetwo parallel planes 844A, 844B may be separated from each other by aseparation distance D that is the minimum distance such that neither ofthe planes 844A, 844B intersects with the central opening 808 of theimplant 800. In embodiments of the invention, the locations of theporous regions 818A, 818B, 818C, 818D may be such that the porousregions 818A, 818B, 818C, 818D are entirely outside of (which may bedescribed as being laterally outboard of) the parallel-plane-boundedregion. Thus, in embodiments of the invention, all of the porous metalregions 818A, 818B, 818C, 818D may be located laterally outboard of thecentral opening 808. More specifically, in an embodiment, as illustratedin FIG. 8M, anterior of the location of maximum width of the centralopening 808, all of the porous material of porous regions 818A, 818B,818C, 818D may be more outboard laterally than those two planes. Inembodiments of the invention, all of the porous metal regions 818A,818B, 818C, 818D may be located laterally outboard of the anchoringscrew holes 820A, 820B. In an embodiment of the invention, there may beno intersection between the porous metal regions 818A, 818B, 818C, 818Dand the anchoring screw holes 820A, 820B.

In an embodiment, the extensions 812, 814 may comprise substantiallysolid metal in some places and porous metal in other places. The porousregion may be present both in the full-height portion of metalliccomponent 810 and in the corresponding extensions 812, 814. Illustratedin FIGS. 8L-8O is one possible configuration of substantially solidmetal and porous metal. In the illustrated configuration, referring to across-section of the extension 812, 814, there may be porous metal 818at the bone-facing surfaces 804A, 804B and extending to some depth intothe extension 812, 814. The extension 812, 814, at its corner where thecentral opening 808 and bone-facing surface 804A or 804B meet, may havesubstantially-solid metal. As is also illustrated, closer to thehorizontal midplane of implant 800, the surface of the extension 812,814 that is opposed to the bone-facing surfaces 804A, 804B, may besubstantially-solid metal.

In an embodiment of the invention, the metallic component 810 may have adowel pin 838 fitting therein, in the extensions 812, 814. The dowel pin838 may have a first end and an opposed second end and a middle regionintermediate between the first end and the second end, and the middleregion of the pin 838 may occupy a hole 842 in the polymeric component840 and the first end of the pin 838 may occupy a first hole 839 in themetallic component 810 and the second end of the pin 838 may occupy asecond hole 839 in the metallic component 810.

Within the metallic component 810, there may be a region ofsubstantially-solid metal into which the dowel pin 838 fits. Thesubstantially-solid region may extend everywhere along the dowel pin 838that has contact with the metallic component 810. As discussed elsewhereherein, providing substantially-solid metal in contact with the dowelpin 838 may be advantageous for achieving the close-tolerancedimensional control that achieves an interference fit of the dowel pin838 with the metallic component 810 and for maintaining the contact ofthe interference fit.

In an embodiment of the invention, at and near the bone-facing surfaceof implant 800, the region of substantially-solid metal 819 thatsurrounds the dowel pin 838 may in turn be surrounded by a porous metalregion 818. This porous metal region 818 may surround thesubstantially-solid dowel-pin-surrounding-region 819 on all exposedsides or surfaces of the dowel-pin-surrounding-region 819. This porousmetal region 818, in turn, may be surrounded by a border or frame 817 ofsubstantially-solid metal. Providing a border or frame 817 ofsubstantially-solid metal may have advantages in terms of providingstructural strength at certain places. FIG. 8L illustrates thesubstantially-solid metal region 816 of anterior component 810 withoutthe presence of the porous metal region 818. It may be thought that thesubstantially-solid region of the anterior component 810 has a recess,defined in part by the frame or border 817, in which the porous region818 exists.

The configuration of porous metal and substantially-solid metal may bedescribed in terms of sequences of materials along certain paths throughimplant 800. FIG. 8N shows such a path that does not go through a dowelpin. FIG. 8N shows that there may be a place in the implant 800 inwhich, along a line or section passing through the implant 800 in agenerally lateral direction, there may be the following sequence ofmaterials: polymeric material; substantially-solid metal; porous metal;substantially-solid metal; the central opening 808; substantially-solidmetal; porous metal; substantially-solid metal; and polymeric material.

FIG. 8O shows such a path that does pass through a dowel pin 838. FIG.8O shows that there may be a place in the implant 800 in which, along aline or section passing through the implant 800 in a generally lateraldirection, there may be the following sequence of materials: polymericmaterial; substantially-solid metal; porous metal; substantially-solidmetal; a pin; substantially-solid metal; porous metal;substantially-solid metal; the central opening 808; substantially-solidmetal; porous metal; substantially-solid metal; a pin;substantially-solid metal; porous metal; substantially-solid metal; andpolymeric material.

Anterior Hole

Referring now to FIG. 8P, in an embodiment of the invention, there maybe provided an anterior hole 850 through the anterior component 810.FIG. 8Q shows a cross-section of implant 800 showing the anterior hole850. In an embodiment, anterior hole 850 may have, in order fromanterior to posterior: an anterior portion 850A, which may be internallythreaded; a middle portion 850B, which may be unthreaded; and aposterior portion 850C, which may be unthreaded. All of these portionsmay have different cross-sectional dimensions and characteristics.

In an embodiment, the anterior portion 850A of the anterior hole 850 mayhave internal threads that are suitable to receive an externallythreaded draw-rod or similar feature or component of an instrument forimplanting the implant 800 at a surgical site.

Middle portion 850B may have an inside diameter that is smaller than theminor diameter of internal threads in anterior portion 850A. It ispossible that middle portion 850B could be omitted.

In an embodiment, the posterior portion of anterior hole 850 may haveposterior recess 850C having an inside diameter that is larger than theinside diameter of the middle portion 850B. If desired, the posteriorrecess inside diameter may be larger than the major diameter of thethreaded anterior portion of the anterior hole 850. The posterior recess850C is shown as being unthreaded, although the absence of threads isnot essential. In an embodiment, the posterior recess 850C may have abase that is perpendicular to the axis of the anterior hole 850 or elseis undercut.

In an embodiment, anterior hole 850 may be preceded anteriorly by ananterior recess 854 in which a portion of a screw retention cover mayreside. Anterior recess 854 may be of generally circular shape orinterrupted circular shape. A screw retention cover may be either ascrew-in screw retention cover 880 or a snap-in screw retention cover890 as described herein. Screw retention cover 880 or 890 may attach tothe implant 800 and can serve to prevent the anchoring screw(s) 828A,828B from backing out, such as may sometimes occur due to repeatedmotion during normal patient activities. For example, in its installedposition, the screw retention cover 880 or 890 may overhang a sufficientportion of the nearby screw holes 820A, 820B to block or prevent exit ofthe heads of screws 828A, 828B. The screw retention cover 880 or 890 canbe attached to the implant 800 after the anchoring screws 828A, 828Bhave been placed in their final installed position, or alternatively thecover 880 or 890 may be present at the time of installation but may bemoved (such as rotated, for example) to its desired locking positionafter the anchoring screws 828A, 828B have been placed in their finalposition.

Threaded Screw Retention Cover

Referring now to FIGS. 8R and 8S, in an embodiment, there may beprovided a threaded screw retention cover 880 that comprises a head 882and a shaft 884. The head 882 may be sufficiently wide to extend over atleast a sufficient portion of the heads of anchoring screws 828A, 828Bto prevent the backing-out of anchoring screws 828A, 828B. The head 882of threaded screw retention cover 880 may be shaped and dimensioned tofit within a recess 854 in the anterior of implant 800, so as to reducean extent that threaded screw retention cover 880 projects into bodilytissue, and the head 882 may have a generally rounded or smoothoutward-facing shape. The shaft 884 may comprise external threads. Theexternal threads may be appropriately dimensioned so as to be able toengage with internally threaded region 850A of the anterior hole 850 ofimplant 800 in order to retain or capture threaded screw retention cover880 in anterior hole 850. Anteriorly, the threaded screw retention cover880 may have a tool-engaging interface suitable for applying torque tothe threaded screw retention cover 880 for purposes of causingengagement with anterior component 810. Such interface may be a socketshaped appropriately to receive a TORX® driver. The threaded screwretention cover 880 could also have a draw-rod interface (notillustrated) to assist in installation of the threaded screw retentioncover 880.

Snap-In Screw Retention Cover

Referring now to FIGS. 8T and 8U, in an embodiment, there may beprovided a snap-in screw retention cover 890. Such cover 890 may, whenin its installed position, cover enough of anchoring screw holes 820A,820B so that anchoring screws 828A, 828B are prevented from backing out.Such cover 890 may engage with anterior hole 850.

In an embodiment, snap-in screw retention cover 890 may comprise a head892 and a post 894 extending therefrom. The head 892 may be sufficientlywide to extend over at least a sufficient portion of the heads ofanchoring screws 828A, 828B to prevent the backing-out of anchoringscrews 828A, 828B. The head 892 may be generally disc-shaped. The head892 may be shaped and dimensioned to fit within a recess 854 in theanterior of implant 800, so as to reduce an extent that snap-in screwretention cover 890 projects into bodily tissue, and head 892 may have agenerally rounded or smooth outward-facing shape. The anterior component810 may comprise a frontal recess 854 that is suitable to receivetherein all or a portion of the head 892 of the snap-in screw retentioncover 890.

Post 894 may be generally suitable to fit within anterior hole 820. Thepost 894 may comprise elastically-deflectable prongs 896A, 896B that canengage with the posterior recess 820C of the anterior hole 820. Post 894may have a generally lengthwise slot to provide two prongs 896A, 896B.The prongs 896A, 896B may be disposed so that their natural undeformedposition is such that the distance between the tips of the prongs 896A,896B is wider than the minor diameter of the threaded portion 820A ofanterior hole 820. At the same time, prongs 896A, 896B may be capable ofelastically bending inward so that the prongs 896A, 896B, includingtheir tips 898 (which may be called beaks), can pass through thethreaded portion 820A and the middle portion 820B of the anterior hole820. There may be an appropriate dimensional relationship between theminor diameter of the threads of the threaded portion 820A, the insidediameter of the middle portion 820B, the width of the slot betweenprongs 896A, 896B, and the excess radial dimension of the tip or beak898, so that when pressed inward the post 894 including the beaks 898are able to pass through the threaded portion 820A and the middleportion 820B of the anterior hole 820, while when the snap-in screwretention cover 890 is sufficiently inserted, the prongs 896A, 896Bincluding their beaks 898 spring outward sufficiently to engage with theposterior recess 820C of the anterior hole 820. The slope of the beaks898, at their posterior surfaces, may be such that beaks 898 can slideover the internal threads of 850A and can slide over the boundarybetween 850A and 850B so as to be forced toward each other as cover 890is being pushed into anterior hole 850. The anterior surface of 850C maybe such that that surface may cooperate with a feature of theoutwardly-springing prongs 896A, 896B so as to engage the prongs 896A,896B with the recess feature 850C. It may be noted that it may bedesirable for the bottom of recess 850C not have a forward taper orsloping feature, because the absence of a forward taper or slopingfeature may make for a more secure engagement of the prongs with therecess.

In an embodiment, the slot in the post 894 may terminate anteriorly in asemi-cylindrical hole shape as illustrated, or, alternatively, the slotmay terminate in a partial hole whose diameter is larger than the widthof the slot 898.

FIG. 8V shows, for an embodiment of the invention, a screw retentioncover in place on implant 800, suitable to prevent backout of screws820A, 820B. The screw retention cover illustrated in FIG. 8V could beeither threaded screw retention cover 880 or snap-in screw retentioncover 890.

Method of Use

In an embodiment of the invention, an implant 800 may be implanted asdescribed herein. If desired, the internal threads of anterior hole 850may be used to engage a draw-rod of an installation instrument. Theimplant 800 may be positioned in its desired location at the surgicalsite. The anchoring screws may be placed and the installation instrumentmay be disengaged, in any order. Then, in one alternative, a cover 880may be placed by screwing it into threads in anterior hole 850. Inanother alternative, a cover 890 may be placed by inserting its post 894into the anterior hole 850 and advancing the cover 890 until its prongs896A, 896B engage with the posterior recess 850C.

Further Comments

Embodiments of the invention provide a combination of surfaces andmaterials that are osseointegrative, each in their own way. It isbelieved that the metal surfaces, which protrude slightly past theadjacent or nearby polymeric surfaces, will most influence the slidingand initial fit of the implant into the intervertebral space and thefeel and tactile feedback to the surgeon upon guiding the implant intoplace. It is believed that this further provides surgeons with usefulfeel and tactile feedback during the surgical procedure. The porousmetal of such surfaces also provides a favorable environment for bone togrow into. During surgery, the patient is generally in a horizontalposition, with no axial compressive load on the spine due to body weightbeing exerted on or borne by the spine. After implantation, when weight(such as weight of some of the patient's body) is exerted on the implantand possibly there is some subsidence of the implant pressing into thevertebrae, there can be contact of bone with both the metal surface andalso the polymeric surface on a particular bone-facing surface of theimplant. In this situation, the geometric pattern of the polymericcomponent becomes active in load transfer and in resisting motion orexpulsion of the implant. The metallic component, especially whateversurfaces of it are porous, can be conducive to osseointegration. Thepolymeric component can contain particles that are osteoconductive orotherwise improve the integration of the polymeric component with bone.Thus, each material or component can have its own role inosseointegration. In combination, the implant may have desirable elasticproperties relative to the elastic properties of bone. In combination,the implant can have desirable radiological properties. However, it isnot wished to be limited to any of this explanation.

Although the polymer has been disclosed as being polyetheretherketone(PEEK) or PEEK in combination with particles of an osseointegrativematerial, it would also be possible to use other polymers, as long assuch other polymer has appropriate structural strength andbiocompatibility, or other polymers in combination with anosseointegrative material. Although the osseointegrative material hasbeen disclosed as being hydroxyapatite, it would also be possible to useother members of the calcium phosphate family, or other appropriatematerial. Specifically, it would be possible to use bioactive glass asthe osseointegrative material. Any chemical or crystallographic form ofcalcium phosphate, or other osseointegrative materials, could also beused. The osseointegrative material could be osteoconductive orosteoinductive. Although the metal has been disclosed as being titaniumor an alloy of titanium, it would also be possible to use other metals,as long as such other metal has appropriate structural strength andbiocompatibility.

It is further possible that the polymeric component could contain anantimicrobial substance. One such possible substance is silver, silvercompounds, or silver nanoparticles. Another possible substance is any ofvarious antibiotics. Any such substance could be mixed together with thepolymer during processing, or could be applied to it as a coating. Suchsubstance could be applied to a metallic component or portion thereof asa coating.

The interior surface of the central opening 106, 206, 306, 406A, 406B,506, 606 may have any or any combination of any or some or all of: asurface of polymeric material (which may contain particles of anosseointegrative material); a surface of a porous metal region; and asurface of a substantially solid metal region. It is believed that ifporous metal is present at an edge of the central opening, the porousmetal may help to encourage bone to “turn the corner” and grow from intothe central opening. It is also possible that, if desired, some of theedge of the central opening may be substantially solid metal as may bedesired for structural strength.

Although the metallic component has been disclosed as possibly having aporous region, it is also possible that the metallic component couldinstead be substantially solid metal having a surface that is roughened.Roughening could be accomplished by methods such as blasting withabrasive or grit, chemical etching, or other methods as known in theart. Porous regions are described as being made by additivemanufacturing techniques such as three-dimensional printing. However,such porous regions could also be made by conventional sintering or byother techniques. Roughening processes could produce surfaces that havea root-mean-square roughness of less than 100 microns. The porous regionmay have a density less than 80% of the metal of which the metalliccomponent is made. Substantially solid metallic regions may have adensity that is more than 90% of the metal of which the metalliccomponent is made. Still further, it is also possible that in a metalliccomponent that has a porous region and a substantially solid region, thesubstantially solid region could be coated or treated by any of thedescribed techniques.

In general, any combination of disclosed features, components andmethods described herein is possible. Steps of a method can be performedin any order that is physically possible.

Although embodiments have been disclosed that are intervertebral spacersfor spinal surgery, it is also possible for similar constructs to beused for other orthopedic implants and applications.

All cited references are incorporated by reference herein.

Although embodiments have been disclosed, it is not desired to belimited thereby. Rather, the scope should be determined only by theappended claims.

We claim:
 1. An implantable device, said device having a device firstbone-facing surface and an opposed device second bone-facing surface andhaving a central opening extending from said device first bone-facingsurface to said device second bone-facing surface, said devicecomprising a metallic component and a remainder of said device, saidmetallic component and said remainder of said device being mechanicallyjoined to each other, said metallic component having a metalliccomponent first bone-facing surface and an opposed metallic componentsecond bone-facing surface, wherein said metallic component comprises ananchoring screw hole passing through an anterior surface of saidmetallic component and continuing at least partially through either saidmetallic component first bone-facing surface or said metallic componentsecond bone-facing surface, said anchoring screw hole having ananchoring screw hole internal surface, wherein either said metalliccomponent first bone-facing surface or said metallic component secondbone-facing surface comprises both a substantially-solid metal regionand a porous metal region, and wherein said porous metal region islocated such that (a) no portion of an anchoring screw hole internalsurface comprises any of said porous metal region; or (b) no more than10% of said anchoring screw hole internal surface comprises said porousmetal region.
 2. The device of claim 1, wherein a front horizontalboundary line is defined as passing through a frontmost place where saidanchoring screw hole internal surface intersects with either of saidbone-facing surfaces, and a rear horizontal boundary line is defined aspassing through a rearmost place where said anchoring screw holeinternal surface intersects with either of said bone-facing surfaces,said front horizontal boundary line and said rear horizontal boundaryline being parallel to each other, and wherein along any horizontal linethat is on either of said bone-facing surfaces between said fronthorizontal boundary line and said rear horizontal boundary line, all ofsaid porous region is laterally further outward from a centerline thanany of said anchoring screw hole internal surface that is on saidhorizontal line on the same side of said centerline.
 3. The device ofclaim 1, wherein said anchoring screw hole internal surface comprises aportion of a sphere.
 4. An implantable device, said device having afirst bone-facing surface and an opposed second bone-facing surface andhaving a central opening extending from said first bone-facing surfaceto said second bone-facing surface, said device comprising a metalliccomponent and a remainder of said device that are mechanically joined toeach other, said metallic component comprising a full-height portion ofsaid metallic component extending continuously from said firstbone-facing surface to said second bone-facing surface, and furthercomprising a superior extension and an inferior extension defining asplit space therebetween, wherein said metallic component comprises aporous metal region that exists, on either said first bone-facingsurface or said second bone-facing surface, in both said full-heightportion of said metallic component and said extension, wherein, oneither said first bone-facing surface or said second bone-facingsurface, said porous metal region is surrounded around its entireperimeter by a frame of substantially-solid metal.
 5. The device ofclaim 4, wherein, on either said first bone-facing surface or saidsecond bone-facing surface, all of said porous metal region is outboard,in a lateral direction, of said central opening.
 6. An implantabledevice, said device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromsaid first bone-facing surface to said second bone-facing surface, saiddevice comprising a metallic component and a remainder of said devicethat are mechanically joined to each other, said metallic componentcomprising a full-height portion of said metallic component extendingcontinuously from said first bone-facing surface to said secondbone-facing surface, and further comprising a superior extension and aninferior extension defining a split space therebetween, wherein saidmetallic component comprises a porous metal region that exists, oneither said first bone-facing surface or said second bone-facingsurface, in both said full-height portion of said metallic component andsaid extension, wherein there are defined two planes that are parallelto each other and are separated by a minimum separation distance toavoid contacting said central opening, and wherein in said full-heightregion any porous metal region is outboard of said respective plane. 7.An implantable device, said device having a first bone-facing surfaceand an opposed second bone-facing surface and having a central openingextending from said first bone-facing surface to said second bone-facingsurface, said device comprising a metallic component and a remainder ofsaid device that are mechanically joined to each other, said metalliccomponent comprising a full-height portion of said metallic componentextending continuously from said first bone-facing surface to saidsecond bone-facing surface, and further comprising a superior extensionand an inferior extension defining a split space therebetween, whereinsaid metallic component comprises a porous metal region that exists, oneither said first bone-facing surface or said second bone-facingsurface, in both said full-height portion of said metallic component andsaid extension, wherein, on either said first bone-facing surface orsaid second bone-facing surface, said porous region further comprises, apin-receiving region that is made of substantially-solid metal and has ahole therethrough suitable to receive a pin, wherein said porous regionextends around all sides of said pin-receiving region.
 8. An implantabledevice, said device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromsaid first bone-facing surface to said second bone-facing surface, saiddevice comprising a metallic component and a remainder of said device,said metallic component and said remainder of said device beingmechanically joined to each other, wherein, said metallic component, insaid first bone-facing surface, comprises a porous metal region, andsaid porous metal region is surrounded on its entire perimeter on saidfirst bone-facing surface by a frame of substantially-solid metal,wherein said metallic component comprises a full-height portion of saidmetallic component extending continuously from said first bone-facingsurface to said second bone-facing surface, and further comprises asuperior extension and an inferior extension defining a split spacetherebetween, and wherein said porous metal region exists in both saidfull-height portion and at least one of said extensions.
 9. The deviceof claim 8, wherein said metallic component further comprises ananchoring screw hole therethrough.
 10. The device of claim 8, whereinsaid porous metal region contains therewithin a first region ofsubstantially-solid metal that is surrounded on its entire perimeter onsaid first bone-facing surface by said porous region.
 11. The device ofclaim 10, wherein said first region of substantially solid metal hastherethrough a hole suitable to be occupied by a pin.
 12. An implantabledevice, said device having a first bone-facing surface and an opposedsecond bone-facing surface and having a central opening extending fromsaid first bone-facing surface to said second bone-facing surface, saiddevice comprising a metallic component and a remainder of said device,said metallic component and said remainder of said device beingmechanically joined to each other, wherein either said first bone-facingsurface or said second bone-facing surface comprises a substantiallysolid metal region and a porous metal region, wherein along a linepassing through said device in a generally lateral direction, there isthe following sequence of materials: polymeric material;substantially-solid metal; porous metal; substantially-solid metal; saidcentral opening; substantially-solid metal; porous metal;substantially-solid metal; and polymeric material.
 13. The device ofclaim 12, wherein along a line passing through said device in agenerally lateral direction, there is the following sequence ofmaterials: polymeric material; substantially-solid metal; porous metal;substantially-solid metal; a first pin; substantially-solid metal;porous metal; substantially-solid metal; said central opening;substantially-solid metal; porous metal; substantially-solid metal; asecond pin; substantially-solid metal; porous metal; substantially-solidmetal; and polymeric material.
 14. The device of claim 12, wherein saidmetallic component further comprises an anchoring screw holetherethrough.